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SubjectRe: [PATCH v2 4/7] clk: Add simple gated clock
Hi Rob,

On Mon, Sep 26, 2011 at 01:33:08PM -0500, Rob Herring wrote:
> Mike,
>
> On 09/22/2011 05:26 PM, Mike Turquette wrote:
> > From: Jeremy Kerr <jeremy.kerr@canonical.com>
> >
> > Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.com>
> > Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
> > Signed-off-by: Jamie Iles <jamie@jamieiles.com>
> > Signed-off-by: Mike Turquette <mturquette@ti.com>
> > ---
> > Changes since v1:
> > Add copyright header
> > Fold in Jamie's patch for set-to-disable clks
> > Use BIT macro instead of shift
> >
> > drivers/clk/Kconfig | 4 ++
> > drivers/clk/Makefile | 1 +
> > drivers/clk/clk-gate.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++
> > include/linux/clk.h | 13 ++++++++
> > 4 files changed, 96 insertions(+), 0 deletions(-)
> > create mode 100644 drivers/clk/clk-gate.c
> >
> > diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
> > index d8313d7..a78967c 100644
> > --- a/drivers/clk/Kconfig
> > +++ b/drivers/clk/Kconfig
> > @@ -12,3 +12,7 @@ config GENERIC_CLK
> > config GENERIC_CLK_FIXED
> > bool
> > depends on GENERIC_CLK
> > +
> > +config GENERIC_CLK_GATE
> > + bool
> > + depends on GENERIC_CLK
> > diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> > index 9a3325a..d186446 100644
> > --- a/drivers/clk/Makefile
> > +++ b/drivers/clk/Makefile
> > @@ -2,3 +2,4 @@
> > obj-$(CONFIG_CLKDEV_LOOKUP) += clkdev.o
> > obj-$(CONFIG_GENERIC_CLK) += clk.o
> > obj-$(CONFIG_GENERIC_CLK_FIXED) += clk-fixed.o
> > +obj-$(CONFIG_GENERIC_CLK_GATE) += clk-gate.o
> > diff --git a/drivers/clk/clk-gate.c b/drivers/clk/clk-gate.c
> > new file mode 100644
> > index 0000000..a1d8e79
> > --- /dev/null
> > +++ b/drivers/clk/clk-gate.c
> > @@ -0,0 +1,78 @@
> > +/*
> > + * Copyright (C) 2010-2011 Canonical Ltd <jeremy.kerr@canonical.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.
> > + *
> > + * Simple clk gate implementation
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/module.h>
> > +#include <asm/io.h>
>
> use linux/io.h
>
> > +
> > +#define to_clk_gate(clk) container_of(clk, struct clk_gate, hw)
> > +
> > +static unsigned long clk_gate_get_rate(struct clk_hw *clk)
> > +{
> > + return clk_get_rate(clk_get_parent(clk->clk));
> > +}
> > +
> > +static void clk_gate_set_bit(struct clk_hw *clk)
> > +{
> > + struct clk_gate *gate = to_clk_gate(clk);
> > + u32 reg;
> > +
> > + reg = __raw_readl(gate->reg);
> > + reg |= BIT(gate->bit_idx);
> > + __raw_writel(reg, gate->reg);
>
> Don't these read-mod-writes need a spinlock around it?
>
> It's possible to have an enable bits and dividers in the same register.
> If you did a set_rate and while doing an enable/disable, there would be
> a problem. Also, it may be 2 different clocks in the same register, so
> the spinlock needs to be shared and not per clock.

Well the prepare lock will be held here and I believe that would be
sufficient.

> > +}
> > +
> > +static void clk_gate_clear_bit(struct clk_hw *clk)
> > +{
> > + struct clk_gate *gate = to_clk_gate(clk);
> > + u32 reg;
> > +
> > + reg = __raw_readl(gate->reg);
> > + reg &= ~BIT(gate->bit_idx);
> > + __raw_writel(reg, gate->reg);
> > +}
> > +
> > +static int clk_gate_enable_set(struct clk_hw *clk)
> > +{
> > + clk_gate_set_bit(clk);
> > +
> > + return 0;
> > +}
> > +
> > +static void clk_gate_disable_clear(struct clk_hw *clk)
> > +{
> > + clk_gate_clear_bit(clk);
> > +}
> > +
> > +struct clk_hw_ops clk_gate_set_enable_ops = {
>
> const?

Yup.

> > + .recalc_rate = clk_gate_get_rate,
> > + .enable = clk_gate_enable_set,
> > + .disable = clk_gate_disable_clear,
> > +};
> > +EXPORT_SYMBOL_GPL(clk_gate_set_enable_ops);
> > +
> > +static int clk_gate_enable_clear(struct clk_hw *clk)
> > +{
> > + clk_gate_clear_bit(clk);
> > +
> > + return 0;
> > +}
> > +
> > +static void clk_gate_disable_set(struct clk_hw *clk)
> > +{
> > + clk_gate_set_bit(clk);
> > +}
>
> Are these wrapper functions really needed? Just assign set_bit and
> clear_bit functions directly to the ops structs. Only the ops struct
> name is exposed to the user.

I used the wrappers because the .enable method has to return an int, but
the disable needs to return void. It's either that or open code the
set/clear in each.

> > +
> > +struct clk_hw_ops clk_gate_set_disable_ops = {
>
> const?

Yes.

Jamie


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