linux-kernel - Re: [alsa-devel] [RFC PATCH] ASoC: wm8731: let codec to manage clock by itself

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Message-ID: <54D104AC.5010603@metafoo.de>
Date:	Tue, 03 Feb 2015 18:26:04 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Mark Brown <broonie@...nel.org>,
	Manuel Lauss <manuel.lauss@...il.com>,
	alsa-devel <alsa-devel@...a-project.org>,
	Richard Purdie <richard@...nedhand.com>,
	patches@...nsource.wolfsonmicro.com,
	LKML <linux-kernel@...r.kernel.org>, linux-sound@...r.kernel.org,
	Manuel Lauss <manuel.lauss@...glemail.com>,
	Bo Shen <voice.shen@...el.com>,
	linux-arm-kernel@...ts.infradead.org,
	Liam Girdwood <lrg@...mlogic.co.uk>
Subject: Re: [alsa-devel] [RFC PATCH] ASoC: wm8731: let codec to manage clock
 by itself

On 02/03/2015 06:17 PM, Russell King - ARM Linux wrote:
> On Tue, Feb 03, 2015 at 05:53:48PM +0100, Lars-Peter Clausen wrote:
>> On 02/03/2015 01:44 PM, Mark Brown wrote:
>>> On Tue, Feb 03, 2015 at 08:54:57AM +0100, Manuel Lauss wrote:
>>>
>>>> +    wm8731->mclk = devm_clk_get(&spi->dev, "mclk");
>>>> +    if (IS_ERR(wm8731->mclk)) {
>>>> +        wm8731->mclk = NULL;
>>>> +        dev_warn(&spi->dev, "assuming static MCLK\n");
>>>> +    }
>>>
>>> This is broken for both deferred probe and in the case where the clock
>>> API genuinely returns a NULL clock.  Other than that it's the kind of
>>> thing that we've done for some other drivers, though it's not good to
>>> have to do this.  Check them for correct behaviour.
>>
>> Ideally we'd introduce a {devm_}clk_get_optional(), with the same semantics
>> as gpiod_get_optional(), which handles the finer details of differentiating
>> between clock specified, but not yet probed, clock specified, but
>> incorrectly and no clock specified, so this doesn't have to be done over and
>> over by each driver.
>
> No, we don't need to.  It clk_get() already knows this distinction, and
> it appropriately returns -ENOENT vs -EPROBE_DEFER according to whether
> there's a clock specified in DT or not.

I know, but it returns a error when no clock is specified (-ENOENT), whereas 
gpiod_get_optional()-like semantics mean, it would return no error.

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