[RFC,PATCH 1/3] Add a common struct clk

[ryan@bluewatersys.com (Ryan Mallon)]

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

Ryan Mallon         		5 Amuri Park, 404 Barbadoes St
ryan at bluewatersys.com         	PO Box 13 889, Christchurch 8013
http://www.bluewatersys.com	New Zealand
Phone: +64 3 3779127		Freecall: Australia 1800 148 751
Fax:   +64 3 3779135			  USA 1800 261 2934