linux-kernel - Re: [PATCH 02/12] ASoC: dapm: Implement stereo mixer control support

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Date:   Thu, 27 Oct 2016 22:02:39 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Chen-Yu Tsai <wens@...e.org>, Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH 02/12] ASoC: dapm: Implement stereo mixer control support

On Thu, Oct 27, 2016 at 1:50 AM, Mark Brown <broonie@...nel.org> wrote:
> On Mon, Oct 03, 2016 at 07:07:54PM +0800, Chen-Yu Tsai wrote:
>
>>       /* find dapm widget path assoc with kcontrol */
>>       dapm_kcontrol_for_each_path(path, kcontrol) {
>> +             /*
>> +              * If status for the second channel was given ( >= 0 ),
>> +              * consider the second and later paths as the second
>> +              * channel.
>> +              */
>> +             if (found && rconnect >= 0)
>> +                     soc_dapm_connect_path(path, rconnect, "mixer update");
>> +             else
>> +                     soc_dapm_connect_path(path, connect, "mixer update");
>>               found = 1;
>> -             soc_dapm_connect_path(path, connect, "mixer update");
>
> This really only works for two channels with the current inteface - the
> comment makes it sound like it'll work for more but we can only pass in
> two (and there's only support for specifying two everywhere).

I could rework it to pass a list of connected status' and the number
of elements instead, but it wouldn't work well for situations where
the number of channels on the kcontrol != the number of paths. I'm not
sure if that's even a valid setup, but it does work with the current
core code.

On the other hand, are there kcontrols that are multi-channel
(> 2 channels)?

I'm inclined to just fixup the comment to make it clear that the
implementation supports stereo, i.e. 2 channels, only.

>
>> -     change = dapm_kcontrol_set_value(kcontrol, val);
>> +     /* This assumes field width < (bits in unsigned int / 2) */
>> +     change = dapm_kcontrol_set_value(kcontrol, val | (rval << width));
>
> That seems like a bit of an assumption in cases where we've got a single
> control for both power and volume?  They're very rare though, I'm not
> even sure any exist.  It'd be good to have a check in the code just in
> case it does come up, it'll likely be a nightmare to debug if someone
> does run into it.

Agreed. I'll put a check and warning before it.

>
> Otherwise I think this makes sense.

Thanks for the review!

Regards
ChenYu