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

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Date:	Fri, 20 May 2011 17:19:56 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Jeremy Kerr <jeremy.kerr@...onical.com>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-sh@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 4/4] clk: Add simple gated clock

On 05/20/2011 02:27 AM, Jeremy Kerr wrote:
> Signed-off-by: Jeremy Kerr<jeremy.kerr@...onical.com>
>
> ---
>   drivers/clk/Kconfig    |    4 ++++
>   drivers/clk/Makefile   |    1 +
>   drivers/clk/clk-gate.c |   41 +++++++++++++++++++++++++++++++++++++++++
>   include/linux/clk.h    |   13 +++++++++++++
>   4 files changed, 59 insertions(+)
>
> diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
> index 0a27963..75d2902 100644
> --- a/drivers/clk/Kconfig
> +++ b/drivers/clk/Kconfig
> @@ -9,3 +9,7 @@ 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..833e0da
> --- /dev/null
> +++ b/drivers/clk/clk-gate.c
> @@ -0,0 +1,41 @@
> +
> +#include<linux/clk.h>
> +#include<linux/module.h>
> +#include<asm/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 int clk_gate_enable(struct clk_hw *clk)
> +{
> +	struct clk_gate *gate = to_clk_gate(clk);
> +	u32 reg;
> +
> +	reg = __raw_readl(gate->reg);
> +	reg |= 1<<  gate->bit_idx;
> +	__raw_writel(reg, gate->reg);

This should be protected with a spinlock for h/w access. You could have 
a mixture of enable bits with divider fields in one register, so the 
enable lock won't help here. However, you would have to find a way to 
have a common spinlock for all accesses to the h/w.

Rob
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