linux-kernel - Re: [RFC,PATCH 1/3] Add a common struct clk

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Message-ID: <4D53B9AC.8020609@bluewatersys.com>
Date:	Thu, 10 Feb 2011 23:10:52 +1300
From:	Ryan Mallon <ryan@...ewatersys.com>
To:	Richard Zhao <richard.zhao@...escale.com>
CC:	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
	Dima Zavin <dmitriyz@...gle.com>,
	Saravana Kannan <skannan@...eaurora.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC,PATCH 1/3] Add a common struct clk

On 10/02/11 23:03, Richard Zhao wrote:
> On Thu, Feb 10, 2011 at 09:21:14AM +1300, Ryan Mallon wrote:
>> On 02/09/2011 07:41 PM, Jeremy Kerr wrote:
>>
>> Hi Jeremy,
>>
>> Couple more comments below.
>>
>> ~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); ?
>>
>>> +     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?
>>
>> 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.
> It's possible to be NULL. So are set_rate/get_rate.
> Ideally, if it's NULL:
> prepare/unprepare: only call parent's prepare/unprepare
> enable/disable: only call parent's enable/disable

No, the whole point of the generic framework is that _all_ clock users 
must call prepare/enable and disable/unprepare. Drivers, etc should not 
rely on underlying knowledge of a platform. This is why, for instance, 
clk_enable will warn if prepare count is zero.

However, I can see that a clock may be fully enabled by its prepare 
function and so the enable function is a no-op. User must still call 
both prepare and enable though. Perhaps this is what you meant?

~Ryan
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