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SubjectRe: [RFC,PATCH 1/3] Add a common struct clk
On 02/15/2011 02:36 PM, Jeremy Kerr wrote:
> Hi Ryan,
>
>>> +int clk_enable(struct clk *clk)
>>> +{
>>> + unsigned long flags;
>>> + int ret = 0;
>>> +
>>> + spin_lock_irqsave(&clk->enable_lock, flags);
>>
>> WARN_ON(clk->prepare_count == 0); ?
>
> Added later, but yes.

Okay, but still failing to understand why this isn't it the first patch.
You are introducing a new file after all.

>>
>>> + if (clk->enable_count == 0 && clk->ops->enable)
>>> + ret = clk->ops->enable(clk);
>>
>> Does it make sense to have a clock with no enable function which still
>> returns success from clk_enable? Do we have any platforms which have
>> NULL clk_enable functions?
>
> It does, yes. Driver code should be always be calling clk_enable before using
> a clock, regardless of the implementation (which it shouldn't have to care
> abut), and should abort their initialisation if the clk_enable() fails.
>
> Some clocks are always running, so the enable op will be empty. This is not an
> error, so the driver is free to continue.
>
>> I think that for enable/disable at least we should require platforms to
>> provide functions and oops if they have failed to do so. In the rare
>> case that a platform doesn't need to do anything for enable/disable they
>> can just supply empty functions.
>
> Sounds like useless boilerplate - it's not an error to not need
> enable/disable, so I don't see why we need to add extra effort to handle this
> case.

I have been convinced that enable/prepare potentially being NULL
callbacks is valid :-).

>
>>> +/**
>>> + * __clk_get - acquire a reference to a clock
>>> + *
>>> + * @clk: The clock to refcount
>>> + *
>>> + * Before a clock is returned from clk_get, this function should be
>>> called + * to update any clock-specific refcounting.
>>
>> This is a bit misleading. It's not "should be called", it "is called". I
>> think you should just remove the documentation for __clk_get/__clk_put
>> or move it into clk.c since the functions are only used internally by
>> the common clock code.
>
> It'd be nice to remove this from the header, but this means we'll need extern
> prototypes in clkdev.c. Might be a reasonable compromise though.

That's probably a better approach anyway, since that makes it blatantly
obvious that the __clk_get and __clk_put functions should not be called
from anywhere except clkdev.c.

>
>>> +/**
>>> + * clk_prepare - prepare clock for atomic enabling.
>>> + *
>>> + * @clk: The clock to prepare
>>> + *
>>> + * Do any blocking initialisation on @clk, allowing the clock to be
>>> later + * enabled atomically (via clk_enable). This function may sleep.
>>
>> "Possibly blocking" as below?
>
> Yep, will unify these (and spell "possibly" correctly :) )

:-)

~Ryan

--
Bluewater Systems Ltd - ARM Technology Solution Centre

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