linux-kernel - Re: Inconsistency in clk framework

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Message-ID: <20121219190824.GX14363@n2100.arm.linux.org.uk>
Date:	Wed, 19 Dec 2012 19:08:24 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Tony Prisk <linux@...sktech.co.nz>
Cc:	Mike Turquette <mturquette@...aro.org>,
	linux-kernel@...r.kernel.org,
	Arm Kernel Mailing List 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Inconsistency in clk framework

On Thu, Dec 20, 2012 at 08:00:49AM +1300, Tony Prisk wrote:
> On Thu, 2012-12-20 at 06:34 +1300, Tony Prisk wrote:
> > On Wed, 2012-12-19 at 09:26 +0000, Russell King - ARM Linux wrote:
> > > On Wed, Dec 19, 2012 at 05:10:33PM +1300, Tony Prisk wrote:
> > > > Hi Mike,
> > > > 
> > > > In attempting to remove some IS_ERR_OR_NULL references, it was pointed
> > > > out that clk_get() can return NULL if CONFIG_HAVE_CLK is not defined.
> > > 
> > > That is correct - but why is that a problem?  As far as users are
> > > concerned, NULL is a valid clock.  If HAVE_CLK is undefined, do you
> > > want all your drivers to suddenly stop working?
> > 
> > That will be where the misunderstanding has occurred - I didn't consider
> > NULL to be a valid clock.
> > 
> > Given that NULL is a valid clock, I guess all tests against get_clk and
> > of_get_clk results should be IS_ERR_OR_NULL. Correct?
> > 
> For the sake of clarity, I should rephrase:
> 
> If the driver can't operate with a NULL clk, it should use a
> IS_ERR_OR_NULL test to test for failure, rather than IS_ERR.

Why should a _consumer_ of a clock care?  It is _very_ important that
people get this idea - to a consumer, the struct clk is just an opaque
cookie.  The fact that it appears to be a pointer does _not_ mean that
the driver can do any kind of dereferencing on that pointer - it should
never do so.
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