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SubjectRe: [PATCH 4/5] clk: Add Baikal-T1 CCU PLLs driver
On Tue, Mar 10, 2020 at 08:30:15AM -0700, Stephen Boyd wrote:
> Quoting Sergey.Semin@baikalelectronics.ru (2020-03-06 05:00:47)
> > From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> >
> > Baikal-T1 is supposed to be supplied with a high-frequency external
> > oscillator. But in order to create signals suitable for each IP-block
> > embedded into the SoC the oscillator output is primarily connected to
> > a set of CCU PLLs. There are five of them to create clocks for the MIPS
> > P5600 cores, the embedded DDR controller, SATA, Ethernet and PCIe
> > domains. The last three domains though named by the biggest system
> > interfaces in fact include nearly all of the rest SoC peripherals.
> > Each of the PLLs is based on True Circuits TSMC CLN28HPM IP-core with
> > an interface wrapper (so called safe PLL' clocks switcher) to simplify
> > the PLL configuration procedure.
> >
> > This driver creates the of-based hardware clocks to use them then in
> > the corresponding subsystems. In order to simplify the driver code we
> > split the functionality up into the PLLs clocks operations and hardware
> > clocks declaration/registration procedures. So if CLK_BT1_CCU is
> > defined, then the first part is available in the kernel, while
> > CLK_BT1_CCU_PLL config makes the actual clocks being registered at the
> > time of_clk_init() is called.
> >
> > Even though the PLLs are based on the same IP-core, they actually may
> > have some differences. In particular, some CCU PLLs supports the output
> > clock change without gating them (like CPU or PCIe PLLs), while the
> > others don't, some CCU PLLs are critical and aren't supposed to be
> > gated. In order to cover all of these cases the hardware clocks driver
> > is designed with a info-descriptor pattern. So there are special static
> > descriptors declared for each PLL, which is then used to create a
> > hardware clock with proper operations. Additionally debugfs-files are
> > provided for each PLL' field to make sure the implemented
> > rate-PLLs-dividers calculation algorithm is correct.
> >
> > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > Signed-off-by: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
> > Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> > Cc: Paul Burton <paulburton@kernel.org>
> > Cc: Ralf Baechle <ralf@linux-mips.org>
>
> > diff --git a/drivers/clk/baikal-t1/Kconfig b/drivers/clk/baikal-t1/Kconfig
> > new file mode 100644
> > index 000000000000..0e2fc86f3ab8
> > --- /dev/null
> > +++ b/drivers/clk/baikal-t1/Kconfig
> > @@ -0,0 +1,35 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +config CLK_BAIKAL_T1
> > + bool "Baikal-T1 Clocks Control Unit interface"
> > + depends on (MIPS_BAIKAL_T1 || COMPILE_TEST) && OF
>
> Does it actually depend on OF for any compilation?

Hm, good question. AFAICS it doesn't. The compilation should work for
both of these configs. While AFAIU it is meaningful to have
(MIPS_BAIKAL_T1 && OF) only instead of making the compile test depending
on the OF as well.

On the other hand MIPS_BAIKAL_T1 indirectly selects OF. I knew about
this reverse dependency, but still preferred to signify that the driver
relies on the OF functionality to properly work. What do you think would
be the best solution in this case:
1) just drop OF, which would mean to have (MIPS_BAIKAL_T1 ||
COMPILE_TEST),
2) redefine the statement to (MIPS_BAIKAL_T1 && OF) || COMPILE_TEST ?

BTW AFAICS OF API is dummy defined if no CONFIG_OF is enabled. So there
is no need in having OF-dependency for any compile-test usecase. Right?
Do you know any case when it's required? For instance, I've found the
similar OF-based conditional statement for CLK_QORIQ,
COMMON_CLK_FIXED_MMIO and COMMON_CLK_KEYSTONE. Do you think these
configs are wrong and have to be fixed by removing the "&& OF" statement
as well?

>
> > + default y
>
> Please no default y. Maybe default MIPS_BAIKAL_T1?

Do you mean that in case if COMPILE_TEST is enabled only, the
drivers below shouldn't be available by default? If so then ok.
I'll use MIPS_BAIKAL_T1 here. If no, then "default y" would be more
appropriate.

>
> > + help
> > + Clocks Control Unit is the core of Baikal-T1 SoC responsible for the
> > + chip subsystems clocking and resetting. It consists of multiple
> > + global clock domains, which can be reset by means of the CCU control
> > + registers. These domains and devices placed in them are fed with
> > + clocks generated by a hierarchy of PLLs, configurable and fixed
> > + dividers. In addition CCU exposes several unrelated functional blocks
> > + like irqless Designware i2c controller with indirectly accessed
> > + registers, AXI bus errors detector, DW PCIe controller PM/clocks/reset
> > + manager, etc.
> > +
> > + This driver provides a set of functions to create the kernel clock
> > + devices of Baikal-T1 PLLs and dividers, and to manipulate the reset
> > + signals of the SoC.
> > +
> > +if CLK_BAIKAL_T1
> > +
> > +config CLK_BT1_CCU_PLL
> > + bool "Baikal-T1 CCU PLLs support"
> > + default y
>
> default MIPS_BAIKAL_T1?

see the comment above.

>
> > + help
> > + Enable this to support the PLLs embedded into the Baikal-T1 SoCs.
> > + These are five PLLs placed at the root of the clocks hierarchy,
> > + right after the external reference osciallator (normally of 25MHz).
> > + They are used to generate a high frequency signals, which are
>
> s/generate a high/generate high/

Ok.

>
> > + either directly wired to the consumers (like CPUs, DDR) or passed
> > + over the clock dividers to be only then used as an individual
> > + reference clocks of a target device.
>
> s/clocks/clock/

Ok.

>
> > +
> > +endif
> > diff --git a/drivers/clk/baikal-t1/ccu-pll.c b/drivers/clk/baikal-t1/ccu-pll.c
> > new file mode 100644
> > index 000000000000..f2087a80b64d
> > --- /dev/null
> > +++ b/drivers/clk/baikal-t1/ccu-pll.c
> > @@ -0,0 +1,474 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 BAIKAL ELECTRONICS, JSC
> > + *
> > + * Authors:
> > + * Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > + * Dmitry Dunaev <dmitry.dunaev@baikalelectronics.ru>
> > + *
> > + * Baikal-T1 CCU PLL interface driver.
> > + */
> > +
> > +#define pr_fmt(fmt) "bt1-ccu-pll: " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/printk.h>
> > +#include <linux/limits.h>
> > +#include <linux/bits.h>
> > +#include <linux/slab.h>
> > +#include <linux/clk-provider.h>
> > +#include <linux/of.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/delay.h>
> > +#include <linux/time64.h>
> > +#include <linux/rational.h>
> > +#include <linux/debugfs.h>
> > +
> > +#include "ccu-pll.h"
> > +#include "common.h"
> > +
> > +#define CCU_PLL_CTL 0x00
> > +#define CCU_PLL_CTL_EN BIT(0)
> > +#define CCU_PLL_CTL_RST BIT(1)
> > +#define CCU_PLL_CTL_CLKR_FLD 2
> > +#define CCU_PLL_CTL_CLKR_MASK GENMASK(7, CCU_PLL_CTL_CLKR_FLD)
> > +#define CCU_PLL_CTL_CLKF_FLD 8
> > +#define CCU_PLL_CTL_CLKF_MASK GENMASK(20, CCU_PLL_CTL_CLKF_FLD)
> > +#define CCU_PLL_CTL_CLKOD_FLD 21
> > +#define CCU_PLL_CTL_CLKOD_MASK GENMASK(24, CCU_PLL_CTL_CLKOD_FLD)
> > +#define CCU_PLL_CTL_BYPASS BIT(30)
> > +#define CCU_PLL_CTL_LOCK BIT(31)
> > +#define CCU_PLL_CTL1 0x04
> > +#define CCU_PLL_CTL1_BWADJ_FLD 3
> > +#define CCU_PLL_CTL1_BWADJ_MASK GENMASK(14, CCU_PLL_CTL1_BWADJ_FLD)
> > +
> > +#define CCU_PLL_RST_DELAY_US 5
> > +#define CCU_PLL_LOCK_DELAY_US(_ref_rate, _nr) ({ \
> > + uint64_t _n = 500ULL * (_nr) * USEC_PER_SEC; \
> > + do_div(_n, _ref_rate); \
> > + _n; \
> > +})
> Can this be a static inline function? We get to learn what the types are
> then.

Ok I'll convert it to the explicit static inline version cause' you asked it.
Personally I don't see the necessity of this here. The arithmetics is
converted to u64, which is more than enough to cover any possible
nr-value.

>
> > +#define CCU_PLL_LOCK_CHECK_RETRIES 50
> > +
> > +#define CCU_PLL_NR_MAX \
> > + ((CCU_PLL_CTL_CLKR_MASK >> CCU_PLL_CTL_CLKR_FLD) + 1)
> > +#define CCU_PLL_NF_MAX \
> > + ((CCU_PLL_CTL_CLKF_MASK >> (CCU_PLL_CTL_CLKF_FLD + 1)) + 1)
> > +#define CCU_PLL_OD_MAX \
> > + ((CCU_PLL_CTL_CLKOD_MASK >> CCU_PLL_CTL_CLKOD_FLD) + 1)
> > +#define CCU_PLL_NB_MAX \
> > + ((CCU_PLL_CTL1_BWADJ_MASK >> CCU_PLL_CTL1_BWADJ_FLD) + 1)
> > +#define CCU_PLL_FDIV_MIN 427000UL
> > +#define CCU_PLL_FDIV_MAX 3500000000UL
> > +#define CCU_PLL_FOUT_MIN 200000000UL
> > +#define CCU_PLL_FOUT_MAX 2500000000UL
> > +#define CCU_PLL_FVCO_MIN 700000000UL
> > +#define CCU_PLL_FVCO_MAX 3500000000UL
> > +#define CCU_PLL_CLKOD_FACTOR 2
> > +
> > +#define CCU_PLL_CALC_FREQ(_ref_rate, _nr, _nf, _od) \
> > + ((_ref_rate) / (_nr) * (_nf) / (_od))
>
> Static inline function please. Does this need to be 64-bit math?

Ok for the same reason. In our platform 32-bit data is enough here.
Though you are right. Some NF may overflow the unsigned long ref_rate
data. I'll add the 64-bit arithmetics in this function too.

BTW I thought about 64-bits here in first place, but then I decided it
may cause the performance drop in ccu_pll_calc_factors() and in
ccu_pll_recalc_rate() so I left the unsigned long calc here.

>
> > +
> > +static int ccu_pll_reset(struct ccu_pll *pll, unsigned long ref_clk,
> > + unsigned long nr)
> > +{
> > + unsigned long ud;
> > + int count;
> > + u32 val;
> > +
> > + ud = CCU_PLL_LOCK_DELAY_US(ref_clk, nr);
> > +
> > + ccu_update(pll->regs + CCU_PLL_CTL, CCU_PLL_CTL_RST, CCU_PLL_CTL_RST);
> > +
> > + count = CCU_PLL_LOCK_CHECK_RETRIES;
> > + do {
> > + udelay(ud);
> > + val = ccu_read(pll->regs + CCU_PLL_CTL);
> > + } while (!(val & CCU_PLL_CTL_LOCK) && --count);
> > +
> > + return (val & CCU_PLL_CTL_LOCK) ? 0 : -ETIMEDOUT;
>
> Looks like readl_poll_timeout().

Nice catch. readl_poll_timeout() perfectly fits here. Though the atomic
version is more appropriate, since the delays are normally small and the
method is executed in the atomic context.

>
> > +}
> > +
> > +static int ccu_pll_enable(struct clk_hw *hw)
> > +{
> > + struct clk_hw *parent_hw = clk_hw_get_parent(hw);
> > + struct ccu_pll *pll = to_ccu_pll(hw);
> > + unsigned long flags;
> > + int ret;
> > + u32 val;
> > +
> > + if (!parent_hw) {
> > + pr_err("Can't enable '%s' with no parent", clk_hw_get_name(hw));
> > + return -EINVAL;
> > + }
> > +
> > + val = ccu_read(pll->regs + CCU_PLL_CTL);
> > + if (val & CCU_PLL_CTL_EN)
> > + return 0;
> > +
> > + spin_lock_irqsave(&pll->regs_lock, flags);
> > + ccu_write(pll->regs + CCU_PLL_CTL, val | CCU_PLL_CTL_EN);
> > + ret = ccu_pll_reset(pll, clk_hw_get_rate(parent_hw),
> > + CCU_GET_FLD(CCU_PLL_CTL_CLKR, val) + 1);
> > + spin_unlock_irqrestore(&pll->regs_lock, flags);
> > + if (ret)
> > + pr_err("PLL '%s' reset timed out\n", clk_hw_get_name(hw));
> > +
> > + return ret;
> > +}
> > +
> > +static void ccu_pll_disable(struct clk_hw *hw)
> > +{
> > + struct ccu_pll *pll = to_ccu_pll(hw);
> > + unsigned long flags;
> > +
> > + spin_lock_irqsave(&pll->regs_lock, flags);
> > + ccu_update(pll->regs + CCU_PLL_CTL, CCU_PLL_CTL_EN, 0);
> > + spin_unlock_irqrestore(&pll->regs_lock, flags);
> > +}
> > +
> > +static int ccu_pll_is_enabled(struct clk_hw *hw)
> > +{
> > + struct ccu_pll *pll = to_ccu_pll(hw);
> > +
> > + return !!(ccu_read(pll->regs + CCU_PLL_CTL) & CCU_PLL_CTL_EN);
> > +}
> > +
> > +static unsigned long ccu_pll_recalc_rate(struct clk_hw *hw,
> > + unsigned long parent_rate)
> > +{
> > + struct ccu_pll *pll = to_ccu_pll(hw);
> > + unsigned long nr, nf, od;
> > + u32 val;
> > +
> > + val = ccu_read(pll->regs + CCU_PLL_CTL);
> > + nr = CCU_GET_FLD(CCU_PLL_CTL_CLKR, val) + 1;
>
> We have FIELD_GET macros for this. Please use them instead of creating
> your own.

Right. I'll use it instead.

>
> > + nf = CCU_GET_FLD(CCU_PLL_CTL_CLKF, val) + 1;
> > + od = CCU_GET_FLD(CCU_PLL_CTL_CLKOD, val) + 1;
> > +
> > + return CCU_PLL_CALC_FREQ(parent_rate, nr, nf, od);
> > +}
> > +
> > +static void ccu_pll_calc_factors(unsigned long rate, unsigned long parent_rate,
> > + unsigned long *nr, unsigned long *nf,
> > + unsigned long *od)
> > +{
> > + unsigned long err, freq, min_err = ULONG_MAX;
> > + unsigned long num, denom, n1, d1, nri;
> > + unsigned long nr_max, nf_max, od_max;
> > +
> > + /*
> > + * Make sure PLL is working with valid input signal (Fdiv). If
> > + * you want to speed the function up just reduce CCU_PLL_NR_MAX.
> > + * This will cause a worse approximation though.
> > + */
> > + nri = (parent_rate / CCU_PLL_FDIV_MAX) + 1;
> > + nr_max = min(parent_rate / CCU_PLL_FDIV_MIN, CCU_PLL_NR_MAX);
> > +
> > + /*
> > + * Find a closest [nr;nf;od] vector taking into account the
> > + * limitations like: 1) 700MHz <= Fvco <= 3.5GHz, 2) PLL Od is
> > + * either 1 or even number within the acceptable range (alas 1s
> > + * is also excluded by the next loop).
> > + */
> > + for (; nri <= nr_max; ++nri) {
> > + /* Use Od factor to fulfill the limitation 2). */
> > + num = CCU_PLL_CLKOD_FACTOR * rate;
> > + denom = parent_rate / nri;
> > +
> > + /*
> > + * Make sure Fvco is within the acceptable range to fulfill
> > + * the condition 1). Note due to the CCU_PLL_CLKOD_FACTOR value
> > + * the actual upper limit is also divided by that factor.
> > + * It's not big problem for us since practically there is no
> > + * need in clocks with that high frequency.
> > + */
> > + nf_max = min(CCU_PLL_FVCO_MAX / denom, CCU_PLL_NF_MAX);
> > + od_max = CCU_PLL_OD_MAX / CCU_PLL_CLKOD_FACTOR;
> > +
> > + /*
> > + * Bypass the out-of-bound values, which can't be properly
> > + * handled by the rational fraction approximation algorithm.
> > + */
> > + if (num / denom >= nf_max) {
> > + n1 = nf_max;
> > + d1 = 1;
> > + } else if (denom / num >= od_max) {
> > + n1 = 1;
> > + d1 = od_max;
> > + } else {
> > + rational_best_approximation(num, denom, nf_max, od_max,
> > + &n1, &d1);
> > + }
> > +
> > + /* Select the best approximation of the target rate. */
> > + freq = (((parent_rate / nri) * n1) / d1);
>
> Please drop extra parenthesis.

Ok. Thanks for noticing this. I'll replace it with ccu_pll_calc_freq() function.

>
> > + err = abs((int64_t)freq - num);
> > + if (err < min_err) {
> > + min_err = err;
> > + *nr = nri;
> > + *nf = n1;
> > + *od = CCU_PLL_CLKOD_FACTOR * d1;
> > + }
> > + }
> > +}
> > +
...
> > +
> > +#ifdef CONFIG_DEBUG_FS
> > +
> > +#define CCU_PLL_DBGFS_BIT_ATTR(_name, _reg, _mask) \
> > +static int ccu_pll_dbgfs_##_name##_get(void *priv, u64 *val) \
> > +{ \
> > + struct ccu_pll *pll = priv; \
> > + \
> > + *val = !!(ccu_read(pll->regs + (_reg)) & (_mask)); \
> > + \
> > + return 0; \
> > +} \
> > +static int ccu_pll_dbgfs_##_name##_set(void *priv, u64 val) \
> > +{ \
> > + struct ccu_pll *pll = priv; \
> > + unsigned long flags; \
> > + \
> > + spin_lock_irqsave(&pll->regs_lock, flags); \
> > + ccu_update(pll->regs + (_reg), (_mask), val ? (_mask) : 0); \
> > + spin_unlock_irqrestore(&pll->regs_lock, flags); \
> > + \
> > + return 0; \
> > +} \
> > +DEFINE_DEBUGFS_ATTRIBUTE(ccu_pll_dbgfs_##_name##_fops, \
> > + ccu_pll_dbgfs_##_name##_get, ccu_pll_dbgfs_##_name##_set, "%llu\n")
> > +
> > +#define CCU_PLL_DBGFS_FLD_ATTR(_name, _reg, _fld, _min, _max) \
> > +static int ccu_pll_dbgfs_##_name##_get(void *priv, u64 *val) \
> > +{ \
> > + struct ccu_pll *pll = priv; \
> > + u32 data; \
> > + \
> > + data = ccu_read(pll->regs + (_reg)); \
> > + *val = CCU_GET_FLD(_fld, data) + 1; \
> > + \
> > + return 0; \
> > +} \
> > +static int ccu_pll_dbgfs_##_name##_set(void *priv, u64 val) \
> > +{ \
> > + struct ccu_pll *pll = priv; \
> > + unsigned long flags; \
> > + u32 data; \
> > + \
> > + val = clamp_t(u64, val, _min, _max); \
> > + data = CCU_SET_FLD(_fld, 0, val - 1); \
> > + \
> > + spin_lock_irqsave(&pll->regs_lock, flags); \
> > + ccu_update(pll->regs + (_reg), _fld ## _MASK, data); \
> > + spin_unlock_irqrestore(&pll->regs_lock, flags); \
> > + \
> > + return 0; \
> > +} \
> > +DEFINE_DEBUGFS_ATTRIBUTE(ccu_pll_dbgfs_##_name##_fops, \
> > + ccu_pll_dbgfs_##_name##_get, ccu_pll_dbgfs_##_name##_set, "%llu\n")
> > +
> > +CCU_PLL_DBGFS_BIT_ATTR(en, CCU_PLL_CTL, CCU_PLL_CTL_EN);
> > +CCU_PLL_DBGFS_BIT_ATTR(rst, CCU_PLL_CTL, CCU_PLL_CTL_RST);
> > +CCU_PLL_DBGFS_FLD_ATTR(nr, CCU_PLL_CTL, CCU_PLL_CTL_CLKR, 1, CCU_PLL_NR_MAX);
> > +CCU_PLL_DBGFS_FLD_ATTR(nf, CCU_PLL_CTL, CCU_PLL_CTL_CLKF, 1, CCU_PLL_NF_MAX);
> > +CCU_PLL_DBGFS_FLD_ATTR(od, CCU_PLL_CTL, CCU_PLL_CTL_CLKOD, 1, CCU_PLL_OD_MAX);
> > +CCU_PLL_DBGFS_BIT_ATTR(bypass, CCU_PLL_CTL, CCU_PLL_CTL_BYPASS);
> > +CCU_PLL_DBGFS_BIT_ATTR(lock, CCU_PLL_CTL, CCU_PLL_CTL_LOCK);
> > +CCU_PLL_DBGFS_FLD_ATTR(nb, CCU_PLL_CTL1, CCU_PLL_CTL1_BWADJ, 1, CCU_PLL_NB_MAX);
> > +
> > +static const struct debugfs_reg32 ccu_pll_dbgfs_regs[] = {
> > + CCU_DBGFS_REG("ctl", CCU_PLL_CTL),
> > + CCU_DBGFS_REG("ctl1", CCU_PLL_CTL1)
> > +};
> > +
> > +static void ccu_pll_debug_init(struct clk_hw *hw, struct dentry *dentry)
> > +{
> > + struct ccu_pll *pll = to_ccu_pll(hw);
> > + struct debugfs_regset32 *regset;
> > +
> > + regset = kzalloc(sizeof(*regset), GFP_KERNEL);
> > + if (!regset)
> > + return;
> > +
> > + regset->regs = ccu_pll_dbgfs_regs;
> > + regset->nregs = ARRAY_SIZE(ccu_pll_dbgfs_regs);
> > + regset->base = pll->regs;
> > + debugfs_create_regset32("registers", 0400, dentry, regset);
> > +
> > + debugfs_create_file_unsafe("en", 0600, dentry, pll,
>
> Why unsafe?

I don't need full proxy file-operations in this case. Moreover since all
fops are defined by means of DEFINE_DEBUGFS_ATTRIBUTE() the set/get
callbacks used will be automatically protected against the corresponding
files removal. See the comment to the debugfs_create_file_unsafe() for
details and commit e7e6198c6056 ("clk: tegra: dfll: Fix debugfs_simple_attr.cocci
warnings") as an example of why unsafe is appropriate here. BTW The commit
has got your SoB.

>
> > + &ccu_pll_dbgfs_en_fops);
> > + debugfs_create_file_unsafe("rst", 0200, dentry, pll,
> > + &ccu_pll_dbgfs_rst_fops);
> > + debugfs_create_file_unsafe("nr", 0600, dentry, pll,
> > + &ccu_pll_dbgfs_nr_fops);
> > + debugfs_create_file_unsafe("nf", 0600, dentry, pll,
> > + &ccu_pll_dbgfs_nf_fops);
> > + debugfs_create_file_unsafe("od", 0600, dentry, pll,
> > + &ccu_pll_dbgfs_od_fops);
> > + debugfs_create_file_unsafe("bypass", 0600, dentry, pll,
> > + &ccu_pll_dbgfs_bypass_fops);
> > + debugfs_create_file_unsafe("lock", 0400, dentry, pll,
> > + &ccu_pll_dbgfs_lock_fops);
> > + debugfs_create_file_unsafe("nb", 0600, dentry, pll,
> > + &ccu_pll_dbgfs_nb_fops);
> > +}
>
> Is there any usage of these outside of development of this driver? I'd
> rather not see us expose blanket register write access with code in
> debugfs. If you're interested in poking register why not use /dev/mem?

These parameters are indeed mostly useful in the driver development. But
they can be useful to diagnose the peripheral device problems like data
corruption or weird clock consumers behaviour. Moreover some of the
parameters aren't utilized by the driver like bypass and nb, but might
be theoretically useful in fixing the problems.

Anyway I do understand your concern regarding write access to these
fields. What about if I implemented the same approach as the one used in
drivers/clk/clk.c? By default the fields are exported in RO-mode.
If a developer needs to debug a clock-based problem one will need to
recompile the driver with #define CLOCK_ALLOW_WRITE_DEBUGFS macro
specified. What do you think?

>
> > +
> > +#else /* !CONFIG_DEBUG_FS */
> > +
> > +#define ccu_pll_debug_init NULL
> > +
> > +#endif /* !CONFIG_DEBUG_FS */
> > +
> > +static const struct clk_ops ccu_pll_gate_to_set_ops = {
> > + .enable = ccu_pll_enable,
> > + .disable = ccu_pll_disable,
> > + .is_enabled = ccu_pll_is_enabled,
> > + .recalc_rate = ccu_pll_recalc_rate,
> > + .round_rate = ccu_pll_round_rate,
> > + .set_rate = ccu_pll_set_rate_norst,
> > + .debug_init = ccu_pll_debug_init
> > +};
> > +
> > +static const struct clk_ops ccu_pll_straight_set_ops = {
> > + .enable = ccu_pll_enable,
> > + .disable = ccu_pll_disable,
> > + .is_enabled = ccu_pll_is_enabled,
> > + .recalc_rate = ccu_pll_recalc_rate,
> > + .round_rate = ccu_pll_round_rate,
> > + .set_rate = ccu_pll_set_rate_reset,
> > + .debug_init = ccu_pll_debug_init
> > +};
> > +
> > +struct ccu_pll *ccu_pll_hw_register(struct ccu_pll_init_data *pll_init)
>
> Can pll_init be const?

Can't believe I missed this. Yes, it can. Thanks.

>
> > +{
> > + struct clk_parent_data parent_data = {0};
> > + struct clk_init_data hw_init = {0};
> > + struct ccu_pll *pll;
> > + int ret;
> > +
> > + if (!pll_init)
> > + return ERR_PTR(-EINVAL);
> > +
> > + pll = kzalloc(sizeof(*pll), GFP_KERNEL);
> > + if (!pll)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + pll->hw.init = &hw_init;
> > + pll->id = pll_init->id;
> > + pll->regs = pll_init->regs;
> > + spin_lock_init(&pll->regs_lock);
> > +
> > + hw_init.name = pll_init->name;
> > + hw_init.flags = CLK_IGNORE_UNUSED;
>
> Why ignore unused? Please have a comment.

Ok. I thought it was obvious, since the flag naming said by itself.
These PLLs are supposed to be left enabled even if they are unused by
any of the drivers. System bootloader makes sure that required clocks
are enabled by default like CPU and DDR PLLs. So we don't want to let
the clock subsystem to disable the PLLs if they are left unused.

>
> > +
> > + if (pll_init->flags & CCU_PLL_GATE_TO_SET) {
> > + hw_init.flags |= CLK_SET_RATE_GATE;
> > + hw_init.ops = &ccu_pll_gate_to_set_ops;
> > + } else {
> > + hw_init.ops = &ccu_pll_straight_set_ops;
> > + }
> > +
> > + if (pll_init->flags & CCU_PLL_CRITICAL)
> > + hw_init.flags |= CLK_IS_CRITICAL;
> > +
> > + if (!pll_init->parent_name) {
> > + ret = -EINVAL;
> > + goto err_free_pll;
> > + }
> > + parent_data.fw_name = pll_init->parent_name;
> > + hw_init.parent_data = &parent_data;
> > + hw_init.num_parents = 1;
> > +
> > + ret = of_clk_hw_register(pll_init->np, &pll->hw);
> > + if (ret)
> > + goto err_free_pll;
> > +
> > + return pll;
> > +
> > +err_free_pll:
> > + kfree(pll);
> > +
> > + return ERR_PTR(ret);
> > +}
> > +
> > +void ccu_pll_hw_unregister(struct ccu_pll *pll)
> > +{
> > + if (!pll)
> > + return;
>
> That would be quite bad. Just let that blow up if so.

Ok.

>
> > +
> > + clk_hw_unregister(&pll->hw);
> > +
> > + kfree(pll);
> > +}
> > diff --git a/drivers/clk/baikal-t1/ccu-pll.h b/drivers/clk/baikal-t1/ccu-pll.h
> > new file mode 100644
> > index 000000000000..6921516311fb
> > --- /dev/null
> > +++ b/drivers/clk/baikal-t1/ccu-pll.h
> > @@ -0,0 +1,73 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2019 BAIKAL ELECTRONICS, JSC
> > + *
> > + * Baikal-T1 CCU PLL interface driver.
> > + */
> > +#ifndef __CLK_BT1_CCU_PLL_H__
> > +#define __CLK_BT1_CCU_PLL_H__
> > +
> > +#include <linux/clk-provider.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/bits.h>
> > +#include <linux/of.h>
> > +
> > +/*
> > + * CCU PLL private flags.
> > + * @CCU_PLL_GATE_TO_SET: Some PLLs output clock can't be changed on-the-fly,
> > + * so according to documentation they need to be gated
> > + * first.
> > + * @CCU_PLL_CRITICAL: Even though there is a way to switch any PLL off, there
> > + * might be some, which shouldn't be in any case.
> > + */
> > +#define CCU_PLL_GATE_TO_SET BIT(0)
> > +#define CCU_PLL_CRITICAL BIT(1)
> > +
> > +/*
> > + * struct ccu_pll_init_data - CCU PLL initialization data.
> > + * @id: Clock private identifier.
> > + * @regs: PLL registers base address.
> > + * @name: Clocks name.
> > + * @parent_name: Clocks parent name in a fw node.
> > + * @np: Pointer to the node describing the CCU PLLs.
> > + * @flags: PLL private flags.
> > + */
> > +struct ccu_pll_init_data {
> > + unsigned int id;
> > + void __iomem *regs;
> > + const char *name;
> > + const char *parent_name;
> > + struct device_node *np;
> > + unsigned long flags;
> > +};
> > +
> > +/*
> > + * struct ccu_pll - CCU PLL descriptor.
>
> Please drop the full stop on title

Ok.

>
> > + * @hw: clk_hw of the PLL.
> > + * @id: Clock private identifier.
> > + * @regs: PLL registers base address.
> > + * @regs_lock: The registers exclusive access spin-lock.
> > + */
> > +struct ccu_pll {
> > + struct clk_hw hw;
> > + unsigned int id;
> > + void __iomem *regs;
> > + spinlock_t regs_lock;
> > +};
> > +#define to_ccu_pll(_hw) container_of(_hw, struct ccu_pll, hw)
> > +
> > +static inline struct clk_hw *ccu_pll_get_clk_hw(struct ccu_pll *pll)
> > +{
> > + return pll ? &pll->hw : NULL;
> > +}
> > +
> > +static inline unsigned int ccu_pll_get_clk_id(struct ccu_pll *pll)
> > +{
> > + return pll ? pll->id : -1;
>
> It's unsigned return value, but return -1? Can this be inlined in the
> one call site and if !pll just continue instead of having to turn it
> into a negative value returned through an unsigned int?

Right, unsigned int, but return -1, which was supposed to be an invalid
value. (unsigned int)-1 => 0xFFFFFFFF is good portable way of setting
FFs to any int.
Anyway your solution seems better. I'll use it instead.

>
> > +}
> > +
> > +extern struct ccu_pll *ccu_pll_hw_register(struct ccu_pll_init_data *init);
> > +
> > +extern void ccu_pll_hw_unregister(struct ccu_pll *pll);
> > +
> > +#endif /* __CLK_BT1_CCU_PLL_H__ */
> > diff --git a/drivers/clk/baikal-t1/clk-ccu-pll.c b/drivers/clk/baikal-t1/clk-ccu-pll.c
> > new file mode 100644
> > index 000000000000..990f0a4a12f9
> > --- /dev/null
> > +++ b/drivers/clk/baikal-t1/clk-ccu-pll.c
> > @@ -0,0 +1,217 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 BAIKAL ELECTRONICS, JSC
> > + *
> > + * Authors:
> > + * Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > + * Dmitry Dunaev <dmitry.dunaev@baikalelectronics.ru>
> > + *
> > + * Baikal-T1 CCU PLL clocks driver.
> > + */
> > +
> > +#define pr_fmt(fmt) "bt1-ccu-pll: " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/printk.h>
> > +#include <linux/slab.h>
> > +#include <linux/clk-provider.h>
> > +#include <linux/of.h>
> > +#include <linux/of_address.h>
> > +#include <linux/ioport.h>
> > +
> > +#include <dt-bindings/clock/bt1-ccu.h>
> > +
> > +#include "ccu-pll.h"
> > +
> > +#define CCU_CPU_PLL_BASE 0x000
> > +#define CCU_SATA_PLL_BASE 0x008
> > +#define CCU_DDR_PLL_BASE 0x010
> > +#define CCU_PCIE_PLL_BASE 0x018
> > +#define CCU_ETH_PLL_BASE 0x020
> > +
> > +#define CCU_PLL_INFO(_id, _name, _pname, _base, _flags) \
> > + { \
> > + .id = _id, \
> > + .name = _name, \
> > + .parent_name = _pname, \
> > + .base = _base, \
> > + .flags = _flags \
> > + }
> > +
> > +#define CCU_PLL_NUM ARRAY_SIZE(pll_info)
> > +
> > +struct ccu_pll_info {
> > + unsigned int id;
> > + const char *name;
> > + const char *parent_name;
> > + unsigned int base;
> > + unsigned long flags;
> > +};
> > +
> > +static const struct ccu_pll_info pll_info[] = {
> > + CCU_PLL_INFO(CCU_CPU_PLL, "cpu_pll", "ref_clk", CCU_CPU_PLL_BASE,
> > + CCU_PLL_CRITICAL),
> > + CCU_PLL_INFO(CCU_SATA_PLL, "sata_pll", "ref_clk", CCU_SATA_PLL_BASE,
> > + CCU_PLL_CRITICAL | CCU_PLL_GATE_TO_SET),
>
> Please comment all CLK_IS_CRITICAL usage

Ok. CPU and DDR PLLs are sources of CPU cores and DDR controller reference clocks,
which obviously shouldn't be ever gated. SATA and PCIe PLLs are the parents of
APB-bus and DDR controller AXI-bus clocks, which if gated would cause
the system being unusable too.

> and don't make your own version
> of the same flags in the common clk framework. Just use the ones in the
> framework.

This was my first design of the clock flags, but then I had to create a
set of custom flags for the CCU dividers driver. That time I turned to
be at a fork either to have two sets of flags: common clock and custom
ones, or a single set of custom flags, some of which then I would
translate to the common clock flags. So I've chosen the latter solution.
I see you suggest the former. Since I was in doubt which one would be
better, I'll implement yours then.

>
> > + CCU_PLL_INFO(CCU_DDR_PLL, "ddr_pll", "ref_clk", CCU_DDR_PLL_BASE,
> > + CCU_PLL_CRITICAL | CCU_PLL_GATE_TO_SET),
> > + CCU_PLL_INFO(CCU_PCIE_PLL, "pcie_pll", "ref_clk", CCU_PCIE_PLL_BASE,
> > + CCU_PLL_CRITICAL),
> > + CCU_PLL_INFO(CCU_ETH_PLL, "eth_pll", "ref_clk", CCU_ETH_PLL_BASE,
> > + CCU_PLL_GATE_TO_SET)
> > +};
> > +
> > +struct ccu_pll_data {
> > + struct device_node *np;
> > + void __iomem *regs;
> > + struct ccu_pll *plls[CCU_PLL_NUM];
> > +};
> > +
> > +static struct ccu_pll *ccu_pll_find_desc(struct ccu_pll_data *data,
> > + unsigned int clk_id)
> > +{
> > + struct ccu_pll *pll;
> > + int idx;
> > +
> > + for (idx = 0; idx < CCU_PLL_NUM; ++idx) {
> > + pll = data->plls[idx];
> > + if (clk_id == ccu_pll_get_clk_id(pll))
> > + return pll;
> > + }
> > +
> > + return ERR_PTR(-EINVAL);
> > +}
> > +
> > +static struct ccu_pll_data *ccu_pll_create_data(struct device_node *np)
> > +{
> > + struct ccu_pll_data *data;
> > +
> > + data = kzalloc(sizeof(*data), GFP_KERNEL);
> > + if (!data)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + data->np = np;
> > +
> > + return data;
> > +}
> > +
> > +static void ccu_pll_free_data(struct ccu_pll_data *data)
> > +{
> > + kfree(data);
> > +}
> > +
> > +static int ccu_pll_request_regs(struct ccu_pll_data *data)
> > +{
> > + data->regs = of_io_request_and_map(data->np, 0,
> > + of_node_full_name(data->np));
> > + if (IS_ERR(data->regs)) {
> > + pr_err("Failed to request PLLs '%s' regs\n",
> > + of_node_full_name(data->np));
> > + return PTR_ERR(data->regs);
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static void ccu_pll_release_regs(struct ccu_pll_data *data)
> > +{
> > + struct resource res;
> > +
> > + iounmap(data->regs);
> > +
> > + /* Try to release the resource as well. */
> > + if (of_address_to_resource(data->np, 0, &res))
> > + return;
> > +
> > + (void)release_mem_region(res.start, resource_size(&res));
> > +}
>
> Instead of having these three functions please inline them at the one call
> site.

This time I disagree. Inlining them won't gain much of the performance
benefit, while combination of weakly coherent code into a single function
will cause worse readability. In my drivers I prefer separating unrelated
or weakly related functionality from each other and creating a set of functions
with coherent code (in this case it's memory allocation for the driver private
data and registers mapping, which are only related in the order of execution).
By this approach I improve the driver code readability making it better
structured. So instead of having a pile of weakly coherent code in the probe
I have a set of work methods and their antagonists (if necessary),
which are called in the required order. Similar design I normally
prefer in callbacks, event handlers, etc, if coherent code can't be
embedded into them.

Moreover I don't see any requirement by which I would have to rearrange the
code in this case, while following my way will perfectly fit to the
kernel coding style described in Documentation/process/coding-style.rst as
"Functions should be short and sweet, and do just one thing." Sorry, I
would prefer to leave this part of the driver being structured as is.

Anyway, this part of the driver will be changed in v2 due to implementing
an alternative approach of Baikal-T1 System Controller DT node design I've
described in RFC: https://lkml.org/lkml/2020/3/22/393 . According to it I
will use a syscon_node_to_regmap(parent) method to get the registers map
from the parental node instead of requesting a dedicated registers range.

>
> > +
> > +static struct clk_hw *ccu_pll_of_clk_hw_get(struct of_phandle_args *clkspec,
> > + void *priv)
> > +{
> > + struct ccu_pll_data *data = priv;
> > + struct ccu_pll *pll;
> > + unsigned int clk_id;
> > +
> > + clk_id = clkspec->args[0];
> > + pll = ccu_pll_find_desc(data, clk_id);
> > + if (IS_ERR(pll)) {
> > + pr_info("Invalid PLL clock ID %d specified\n", clk_id);
> > + return ERR_CAST(pll);
> > + }
> > +
> > + return ccu_pll_get_clk_hw(pll);
> > +}
> > +
> > +static int ccu_pll_clk_register(struct ccu_pll_data *data)
> > +{
> > + int idx, ret;
> > +
> > + for (idx = 0; idx < CCU_PLL_NUM; ++idx) {
> > + const struct ccu_pll_info *info = &pll_info[idx];
> > + struct ccu_pll_init_data init = {0};
> > +
> > + init.id = info->id;
> > + init.regs = data->regs + info->base;
> > + init.parent_name = info->parent_name;
> > + init.np = data->np;
> > + init.flags = info->flags;
> > +
> > + ret = of_property_read_string_index(data->np,
> > + "clock-output-names", init.id, &init.name);
>
> Do you need this property ever? It would be nice to not have it if
> possible.

It isn't needed other than to provide a custom output clock names for the
predefined set of clocks. I've seen it has been used for this purpose in
many drivers of the common clk subsystem. Is this enough to have it
supported in the driver or should I remove it anyway?

>
> > + if (ret)
> > + init.name = info->name;
> > +
> > + data->plls[idx] = ccu_pll_hw_register(&init);
> > + if (IS_ERR(data->plls[idx])) {
> > + ret = PTR_ERR(data->plls[idx]);
> > + pr_err("Couldn't register PLL hw '%s'\n",
> > + init.name);
> > + goto err_hw_unregister;
> > + }
> > + }
> > +
> > + ret = of_clk_add_hw_provider(data->np, ccu_pll_of_clk_hw_get, data);
> > + if (ret) {
> > + pr_err("Couldn't register PLL provider of '%s'\n",
> > + of_node_full_name(data->np));
> > + goto err_hw_unregister;
> > + }
> > +
> > + return 0;
> > +
> > +err_hw_unregister:
> > + for (--idx; idx >= 0; --idx)
> > + ccu_pll_hw_unregister(data->plls[idx]);
> > +
> > + return ret;
> > +}
> > +
> > +static __init void ccu_pll_init(struct device_node *np)
> > +{
> > + struct ccu_pll_data *data;
> > + int ret;
> > +
> > + data = ccu_pll_create_data(np);
> > + if (IS_ERR(data))
> > + return;
> > +
> > + ret = ccu_pll_request_regs(data);
> > + if (ret)
> > + goto err_free_data;
> > +
> > + ret = ccu_pll_clk_register(data);
> > + if (ret)
> > + goto err_release_regs;
> > +
> > + pr_info("CCU CPU/SATA/DDR/PCIe/Ethernet PLLs are initialized\n");
>
> Please don't have I'm alive probe messages at info level. Just slows
> down boot for developer comfort.

Ok.

>
> > +
> > + return;
> > +
> > +err_release_regs:
> > + ccu_pll_release_regs(data);
> > +
> > +err_free_data:
> > + ccu_pll_free_data(data);
> > +}
> > +CLK_OF_DECLARE(ccu_pll, "be,bt1-ccu-pll", ccu_pll_init);
>
> Any reason this can't be a platform device driver?

I thought it was normal to have the clock devices available as early
as possible. Especially when it comes to the system-wide PLLs and dividers.
So the question is kind of surprising for me.

Anyway in my case the platform-specific code is using the CPU PLLs rate
to get the MIPS count/compare timer reference clock. At least due to this
the PLL clock providers must be available at the system initialization stage.
Platform device probe stage wouldn't work for us here.

Moreover we can't rely on the order of the devices probe procedure, because
the CCU PLLs and CCU dividers will be sub-nodes of the Baikal-T1 System Controller,
which will be a sub-node of the APB-bus node consuming the corresponding CCU
divider clock. The CCU PLL and divider clocks are utilized literally by each
device in the system, so there might be too many PROBE_DEFER errors before we get
to the clock devices binding with drivers.

To sum up I'd leave both PLL, AXI-bus and System device dividers
clocks being populated in the init stage by means of the CLK_OF_DECLARE
macro.

>
> > diff --git a/drivers/clk/baikal-t1/common.h b/drivers/clk/baikal-t1/common.h
> > new file mode 100644
> > index 000000000000..07c8d67f5275
> > --- /dev/null
> > +++ b/drivers/clk/baikal-t1/common.h
> > @@ -0,0 +1,44 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2019 BAIKAL ELECTRONICS, JSC
> > + *
> > + * Baikal-T1 CCU common methods.
> > + */
> > +#ifndef __CLK_BT1_COMMON_H__
> > +#define __CLK_BT1_COMMON_H__
> > +
> > +#include <linux/debugfs.h>
> > +#include <linux/io.h>
> > +
> > +#define CCU_GET_FLD(_name, _data) \
> > + (((u32)(_data) & _name ## _MASK) >> _name ## _FLD)
> > +
> > +#define CCU_SET_FLD(_name, _data, _val) \
> > + (((u32)(_data) & ~_name ## _MASK) | \
> > + (((u32)(_val) << _name ## _FLD) & _name ## _MASK))
> > +
> > +#define CCU_DBGFS_REG(_name, _off) \
> > +{ \
> > + .name = _name, \
> > + .offset = _off \
> > +}
> > +
> > +static inline u32 ccu_read(void __iomem *reg)
> > +{
> > + return readl(reg);
> > +}
> > +
> > +static inline void ccu_write(void __iomem *reg, u32 data)
> > +{
> > + writel(data, reg);
> > +}
> > +
> > +static inline void ccu_update(void __iomem *reg, u32 mask, u32 data)
> > +{
> > + u32 old;
> > +
> > + old = readl_relaxed(reg);
> > + writel((old & ~mask) | (data & mask), reg);
> > +}
>
> Please just write the code in line as readl/writel/etc. This whole file
> doesn't look necessary.

Agreed.

---
Stephen, thank you very much for the very thorough review. v2 will be
sent shortly after I get answers to a few question I've asked in this
message, after I fix the issues you raised here and get to refactor
the System Controller DT node design described in the RFC
(https://lkml.org/lkml/2020/3/22/393). Should you have any comments
regarding it please reply right to the RFC. You must have received a
copy in your email.

I'll also do my best to take into account the fixes suggested here by you
in [Patch 5/5] "clk: Add Baikal-T1 CCU dividers driver" of this
patchset.

Regards,
-Sergey

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