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

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Date:	Mon, 26 Sep 2011 13:33:08 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Mike Turquette <mturquette@...com>
CC:	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

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.

> +}
> +
> +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?

> +	.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.

> +
> +struct clk_hw_ops clk_gate_set_disable_ops = {

const?

Rob

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