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

[Lars-Peter Clausen <lars@metafoo.de>]

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.