linux-kernel - Re: [PATCH V1] ASoC: fsl_ssi: refine ipg clock usage in this module

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Date:	Tue, 9 Sep 2014 13:27:10 -0700
From:	Nicolin Chen <nicoleotsuka@...il.com>
To:	Timur Tabi <timur@...i.org>
Cc:	Shengjiu Wang <shengjiu.wang@...escale.com>,
	Li.Xiubo@...escale.com, lgirdwood@...il.com, broonie@...nel.org,
	perex@...ex.cz, tiwai@...e.de, alsa-devel@...a-project.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	mpa@...gutronix.de
Subject: Re: [PATCH V1] ASoC: fsl_ssi: refine ipg clock usage in this module

On Tue, Sep 09, 2014 at 03:03:53PM -0500, Timur Tabi wrote:
> On 09/09/2014 02:59 PM, Nicolin Chen wrote:
> >+	/*
> >+	 * Initially mark the clock to NULL for all platforms so that later
> >+	 * clk_prepare_enable() will ignore and return 0 for non-clock cases.
> >+	 */
> >+	ssi_private->clk = NULL;
> 
> According to Mark, NULL is a valid clock, so this should be instead:
> 
> 	ssi_private->clk = PTR_ERR(-EINVAL);
> 
> although that doesn't sit well with me.

I guess Mark's comment is merely against the check for clk validation
because if talking about clk validation, we should check IS_ERR(clk)
rather than check !=NULL directly.

However, my approach doesn't need any check. The open() or pm_resume()
can just call clk_prepare_enable() directly. The __clk_enable() will
then handle the 'clk == NULL' case:

static int __clk_enable(struct clk *clk)
{
	int ret = 0;

	if (!clk)
		return 0;
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