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    SubjectRe: [RFC][PATCH 1/2] ARM: OMAP4: clock: Add device tree support for AUXCLKs
    On 04/11/2013 10:48 AM, Roger Quadros wrote:
    > On 04/10/2013 08:39 PM, Nishanth Menon wrote:
    >> On 13:55-20130410, Roger Quadros wrote:
    >>> On 04/10/2013 11:06 AM, Mike Turquette wrote:
    >>>> Quoting Nishanth Menon (2013-04-09 13:49:00)
    >>>>> On 10:43-20130409, Tony Lindgren wrote:
    >>>>>> * Tony Lindgren <tony@atomide.com> [130409 09:54]:
    >>>>>>> * Roger Quadros <rogerq@ti.com> [130409 03:00]:
    >>>>>>>> On 04/05/2013 06:58 PM, Tony Lindgren wrote:
    >>>>>>>>> Can't you just use the clock name there to get it?
    >>>>>>>> In device tree we don't pass around clock names. You can either get
    >>>>>>>> a phandle or an index to the clock.
    >>>>>>>>
    >>>>>>>> e.g. Documentation/devicetree/bindings/clock/imx31-clock.txt
    >>>>>>> Yes I understand that. But the driver/clock/omap driver can just
    >>>>>>> remap the DT device initially so the board specific clock is
    >>>>>>> found from the clock alias table. Basically initially a passthrough
    >>>>>>> driver that can be enhanced to parse DT clock bindings and load
    >>>>>>> data from /lib/firmware.
    >>>>>> Actually probably the driver/clock/omap can even do even less
    >>>>>> initially. There probably even no need to remap clocks there.
    >>>>>>
    >>>>>> As long as the DT clock driver understands that a board specific
    >>>>>> auxclk is specified in the DT it can just call clk_add_alias() so
    >>>>>> the driver will get the right auxclk from cclock44xx_data.c.
    >>>>>>
    >>>>>> Then other features can be added later on like to allocate a
    >>>>>> clock entirely based on the binding etc.
    >>>>> I did try to have an implementation for cpufreq using clock nodes.
    >>>>> unfortunately, device tree wont let me have arguments of strings :(
    >>>>> So, I am unable to do clock = <&clk mpu_dpll>;
    >>>>> instead, I am forced to do clock = <&clk 249>;
    >>>>>
    >>>> See http://article.gmane.org/gmane.linux.ports.arm.kernel/229034
    >>>>
    >>> Awesome. Thanks for pointing this out Mike.
    >>>
    >>> Now all we need to do is create a named define for each clock index in the
    >>> header file.
    >> Approach #3: Thanks to Tony for collaborating on this:
    >> Works for cpufreq-cpu0 - additional patches:
    >> http://pastebin.com/GHnTRVJf, http://pastebin.com/FZS89J6L (tested on
    >> beagleXM)
    >> Work for USB - http://pastebin.com/aJpDnXci - thanks Roger for testing
    >> this.
    >> Details in the patch below (Tony, I have added you as collaborator for
    >> helping in getting this working-clk_add_alias was'nt needed in the
    >> internal patch discussion we had - I have taken a bit of freedom in
    >> adding your contributions to the patch below)
    >>
    >> Folks, this does seem to be the best compromise we can achieve at this
    >> point in time. feedback on this approach is much appreciated - if folks
    >> are ok, I can post this as an formal patch series.
    > This looks fine to me. Minor comments below.

    I like it. No IDs and can add clocks support in DT as needed.

    >
    >> From 130a41821bf57081ca45ef654029175d173135e6 Mon Sep 17 00:00:00 2001
    >> From: Nishanth Menon <nm@ti.com>
    >> Date: Tue, 9 Apr 2013 19:26:40 -0500
    >> Subject: [RFC PATCH] clk: OMAP: introduce device tree binding to kernel clock
    >> data
    >>
    >> OMAP clock data is located in arch/arm/mach-omap2/cclockXYZ_data.c.
    >> However, this presents an obstacle for using these clock nodes in
    >> Device Tree definitions. There are many possible approaches to this
    >> problem as discussed in the following thread:
    >> http://marc.info/?t=136370325600009&r=1&w=2
    >> Highlights of the options:
    >> a) device specific clk_add_alias:
    >> cons: driver handling required
    >> b) using an generic clk node and indexing to reach the clock required.
    >> This is similar in approach taken by tegra and few other platforms.
    >> example clock = <&clk 5>;
    >> cons: potential to have mismatches in indexed table and associated
    >> dtb data. In addition, managing continued documentation in bindings
    >> as clock indexing increases. Even though readability angle could be
    >> improved by using preprocessing of DT using macros, indexed approach
    >> is inherently risky from cases like the following:
    >> clk indexes in kernel:
    >> 1 - mpu_dpll
    >> 2 - aux_clk1
    >> 3 - core_clk
    >> DT entry for peripheral x uses <&clk 2>, kernel updates to:
    >> 1 - mpu_dpll
    >> 2 - per_dpll
    >> 3 - aux_clk1
    >> 4 - core_clk
    >> using the old dtb(or dts missing an update), on new kernel which has
    >> updated indices will result in per_dpll now controlled for peripheral
    >> X without warning or any potential error detection and warning.
    >>
    >> Even though we can claim this is user error, such errors are hard to
    >> track down and fix.
    >>
    >> An alternate approach introduced here is to introduce device tree bindings
    >> corresponding to the clock nodes required in DT definition for SoC which
    >> automatically maps back to the definitions in cclockXYZ_data.c.
    >>
    >> The driver introduced here to do this mapping will eventually be the
    >> place where the clock handling will migrate to. We need to consider this
    >> angle as well so that the solution will be an valid transition point for
    >> moving the clock data out of kernel image (into device tree or firmware load
    >> etc..).
    >>
    >> Overall strategy introduced here is simple: an clock node described in
    > typo: "an"->"a"
    >
    >> device tree blob is used to identify the exact clock provided in the SoC
    >> specific data. This is then linked back using of_clk_add_provider to the
    >> device node to be accessible by of_clk_get.
    >>
    >> Based on discussion contributions from Roger Quadros, Grygorii Strashko
    >> and others.
    >>
    >> [tony@atomide.com: co-developed]
    >> Signed-off-by: Tony Lindgren <tony@atomide.com>
    >> Signed-off-by: Nishanth Menon <nm@ti.com>
    >> ---
    >> .../devicetree/bindings/clock/omap-clock.txt | 40 +++++++++
    >> drivers/clk/Makefile | 1 +
    >> drivers/clk/omap/Makefile | 1 +
    >> drivers/clk/omap/clk.c | 94 ++++++++++++++++++++
    >> 4 files changed, 136 insertions(+)
    >> create mode 100644 Documentation/devicetree/bindings/clock/omap-clock.txt
    >> create mode 100644 drivers/clk/omap/Makefile
    >> create mode 100644 drivers/clk/omap/clk.c
    >>
    >> diff --git a/Documentation/devicetree/bindings/clock/omap-clock.txt b/Documentation/devicetree/bindings/clock/omap-clock.txt
    >> new file mode 100644
    >> index 0000000..07e3ff8
    >> --- /dev/null
    >> +++ b/Documentation/devicetree/bindings/clock/omap-clock.txt
    >> @@ -0,0 +1,40 @@
    >> +Device Tree Clock bindings for Texas Instrument's OMAP compatible platforms
    >> +
    >> +This binding is a work-in-progress, and meant to be stage #1 of transitioning
    >> +OMAP clock data out of kernel image.
    >> +
    >> +This binding uses the common clock binding[1].
    >> +
    >> +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
    >> +
    >> +Required properties:
    >> +- compatible : shall be "ti,omap-clock"
    >> +- #clock-cells : from common clock binding; shall be set to 0.
    >> +NOTE:
    >> +node name should map to clock database in arch/arm/mach-omap2/cclock<SoC>_data.c
    >> +Since all clocks are described with _ck, the node name is optimized to drop the
    >> +usage of _ck. For example, a clock called dpll1_ck will be defined as dpll1.
    >> +
    >> +Example #1: describing clock node for CPU on OMAP34xx platform:
    >> +Ref: arch/arm/mach-omap2/cclock3xxx_data.c
    >> +describes the CPU clock to be as follows
    >> + CLK(NULL, "dpll1_ck", &dpll1_ck, CK_3XXX),
    >> +Corresponding binding will be:
    >> + dpll1: dpll1 {
    >> + #clock-cells = <0>;
    >> + compatible = "ti,omap-clock";
    >> + };
    >> +And it's usage will be:
    >> + clocks = <&dpll1>;
    >> +
    >> +Example #2: describing clock node for auxilary clock #3 on OMAP443x platform:
    >> +Ref: arch/arm/mach-omap2/cclock44xx_data.c
    >> +describes the auxclk3 clock to be as follows:
    >> + CLK(NULL, "auxclk3_ck", &auxclk3_ck, CK_443X),
    >> +Corresponding binding will be:
    >> + auxclk3: auxclk3 {
    >> + #clock-cells = <1>;
    >> + compatible = "ti,omap-clock";
    >> + };
    >> +And it's usage will be:
    >> + clocks = <&auxclk3>;
    >> diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
    >> index 300d477..a0209d7 100644
    >> --- a/drivers/clk/Makefile
    >> +++ b/drivers/clk/Makefile
    >> @@ -27,6 +27,7 @@ obj-$(CONFIG_ARCH_U8500) += ux500/
    >> obj-$(CONFIG_ARCH_VT8500) += clk-vt8500.o
    >> obj-$(CONFIG_ARCH_ZYNQ) += clk-zynq.o
    >> obj-$(CONFIG_ARCH_TEGRA) += tegra/
    >> +obj-$(CONFIG_ARCH_OMAP) += omap/
    >>
    >> obj-$(CONFIG_X86) += x86/
    >>
    >> diff --git a/drivers/clk/omap/Makefile b/drivers/clk/omap/Makefile
    >> new file mode 100644
    >> index 0000000..8195931
    >> --- /dev/null
    >> +++ b/drivers/clk/omap/Makefile
    >> @@ -0,0 +1 @@
    >> +obj-y += clk.o
    >> diff --git a/drivers/clk/omap/clk.c b/drivers/clk/omap/clk.c
    >> new file mode 100644
    >> index 0000000..63a4cce
    >> --- /dev/null
    >> +++ b/drivers/clk/omap/clk.c
    >> @@ -0,0 +1,94 @@
    >> +/*
    >> + * Texas Instruments OMAP Clock driver
    >> + *
    >> + * Copyright (C) 2013 Texas Instruments Incorporated - http://www.ti.com/
    >> + * Nishanth Menon
    > missing e-mail id.
    >
    >> + * Tony Lindgren <tony@atomide.com>
    >> + *
    >> + * This program is free software; you can redistribute it and/or modify
    >> + * it under the terms of the GNU General Public License version 2 as
    >> + * published by the Free Software Foundation.
    >> + *
    >> + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
    >> + * kind, whether express or implied; without even the implied warranty
    >> + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    >> + * GNU General Public License for more details.
    >> + */
    >> +
    >> +#include <linux/clkdev.h>
    >> +#include <linux/clk-private.h>
    >> +#include <linux/kernel.h>
    >> +#include <linux/module.h>
    >> +#include <linux/of_device.h>
    >> +#include <linux/platform_device.h>
    >> +#include <linux/string.h>
    >> +
    >> +static const struct of_device_id omap_clk_of_match[] = {
    >> + {.compatible = "ti,omap-clock",},
    >> + {},
    >> +};
    >> +
    >> +MODULE_DEVICE_TABLE(of, omap_clk_of_match);
    >> +
    > Is this driver ever going to be a loadable module? If not then you don't need this.
    >
    >> +/**
    >> + * omap_clk_probe() - create link from DT definition to clock data
    >> + * @pdev: device node
    >> + *
    >> + * REVISIT: We are now assuming the following:
    >> + * 1. omap clock names end with _ck
    >> + * 2. omap clocks don't get removed
    >> + */
    >> +static int omap_clk_probe(struct platform_device *pdev)
    >> +{
    >> + struct clk *clk;
    >> + int res;
    >> +
    >> + const struct of_device_id *match;
    >> + struct device_node *np = pdev->dev.of_node;
    >> + char clk_name[32];
    >> +
    >> + match = of_match_device(omap_clk_of_match, &pdev->dev);
    >> +
    >> + /* Set up things so consumer can call clk_get() with name */
    >> + snprintf(clk_name, 32, "%s_ck", np->name);
    >> + clk = clk_get(NULL, clk_name);
    >> + if (IS_ERR(clk)) {
    >> + res = PTR_ERR(clk);
    >> + dev_err(&pdev->dev, "could not get clock %s (%d)\n",
    >> + clk_name, res);
    >> + goto out;
    >> + }
    >> +
    >> + /* This allows the driver to of_clk_get() */
    >> + res = of_clk_add_provider(np, of_clk_src_simple_get, clk);
    >> + if (res)
    >> + dev_err(&pdev->dev, "could not add provider for %s (%d)\n",
    >> + clk_name, res);
    >> +
    >> + clk_put(clk);
    >> +out:
    >> + return res;
    >> +}
    >> +
    >> +MODULE_ALIAS("platform:omap_clk");
    > ditto.
    >
    >> +
    >> +/* We assume here that OMAP clocks will not be removed */
    >> +static struct platform_driver omap_clk_driver = {
    >> + .probe = omap_clk_probe,
    >> + .driver = {
    >> + .name = "omap_clk",
    >> + .owner = THIS_MODULE,
    > same here.
    >
    >> + .of_match_table = of_match_ptr(omap_clk_of_match),
    >> + },
    >> +};
    >> +
    >> +static int __init omap_clk_init(void)
    >> +{
    >> + return platform_driver_register(&omap_clk_driver);
    >> +}
    >> +
    >> +arch_initcall(omap_clk_init);
    >> +
    >> +MODULE_DESCRIPTION("OMAP Clock driver");
    >> +MODULE_AUTHOR("Texas Instruments Inc.");
    >> +MODULE_LICENSE("GPL v2");
    >>
    > cheers,
    > -roger

    -grygorii


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