linux-kernel - Re: [PATCH v2 4/7] clk: Add simple gated clock

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Date:	Mon, 26 Sep 2011 19:40:24 +0100
From:	Jamie Iles <jamie@...ieiles.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Mike Turquette <mturquette@...com>, linux-kernel@...r.kernel.org,
	paul@...an.com, linaro-dev@...ts.linaro.org,
	linus.walleij@...ricsson.com, patches@...aro.org,
	eric.miao@...aro.org, broonie@...nsource.wolfsonmicro.com,
	magnus.damm@...il.com, arnd.bergmann@...aro.org,
	Jamie Iles <jamie@...ieiles.com>, skannan@...cinc.com,
	linux@....linux.org.uk, jeremy.kerr@...onical.com,
	tglx@...utronix.de, linux-arm-kernel@...ts.infradead.org,
	sboyd@...inc.com
Subject: Re: [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@...onical.com>
> > 
> > Signed-off-by: Jeremy Kerr <jeremy.kerr@...onical.com>
> > Signed-off-by: Mark Brown <broonie@...nsource.wolfsonmicro.com>
> > Signed-off-by: Jamie Iles <jamie@...ieiles.com>
> > Signed-off-by: Mike Turquette <mturquette@...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@...onical.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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