Date: Tue, 22 Jun 2010 07:43:10 +0300
From: Baruch Siach <baruch@tkos.co.il>
To: Jeremy Kerr <jeremy.kerr@canonical.com>
Cc: linux-kernel@vger.kernel.org, Ben Herrenchmidt <benh@kernel.crashing.org>,
       linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/2] Add a common struct clk
Message-ID: <20100622044310.GB26865@jasper.tkos.co.il>
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Hi Jeremy,

On Mon, Jun 21, 2010 at 01:35:13PM +0800, Jeremy Kerr wrote:
> We currently have 21 definitions of struct clk in the ARM architecture,
> each defined on a per-platform basis. This makes it difficult to define
> platform- (or architecture-) independent clock sources without making
> assumptions about struct clk, and impossible to compile two
> platforms with different struct clks into a single image.
> 
> This change is an effort to unify struct clk where possible, by defining
> a common struct clk, containing a set of clock operations. Different
> clock implementations can set their own operations, and have a standard
> interface for generic code. The callback interface is exposed to the
> kernel proper, while the clock implementations only need to be seen by
> the platform internals.
> 
> This allows us to share clock code among platforms, and makes it
> possible to dynamically create clock devices in platform-independent
> code.
> 
> Platforms can enable the generic struct clock through
> CONFIG_USE_COMMON_STRUCT_CLK. In this case, the clock infrastructure
> consists of a common struct clk:
> 
> struct clk {
> 	const struct clk_ops	*ops;
> 	unsigned int		enable_count;
> 	struct mutex		mutex;
> };
> 
> And a set of clock operations (defined per type of clock):
> 
> struct clk_operations {

That's clk_ops above, and in the code.

>        int             (*enable)(struct clk *);
>        void            (*disable)(struct clk *);
>        unsigned long   (*get_rate)(struct clk *);
>        [...]
> };
> 
> To define a hardware-specific clock, machine code can "subclass" the
> struct clock into a new struct (adding any device-specific data), and
> provide a set of operations:
> 
> struct clk_foo {
> 	struct clk	clk;
> 	void __iomem	*some_register;
> };
> 
> struct clk_operations clk_foo_ops = {

Ditto.

> 	.get_rate = clk_foo_get_rate,
> };
> 
> The common clock definitions are based on a development patch from Ben
> Herrenschmidt <benh@kernel.crashing.org>.
> 
> Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.com>

baruch

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