linux-kernel - Re: [RFC PATCH v1 2/2] ASoC: dapm: add support for preparing streams

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Message-ID: <1jsepw9fl2.fsf@starbuckisacylon.baylibre.com>
Date: Mon, 06 Jan 2025 15:34:01 +0100
From: Jerome Brunet <jbrunet@...libre.com>
To: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc: linux-sound@...r.kernel.org,  linux-amlogic@...ts.infradead.org,
  s.nawrocki@...sung.com,  lgirdwood@...il.com,  broonie@...nel.org,
  linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 2/2] ASoC: dapm: add support for preparing streams

On Mon 06 Jan 2025 at 15:28, Jerome Brunet <jbrunet@...libre.com> wrote:

> On Mon 06 Jan 2025 at 15:13, Martin Blumenstingl <martin.blumenstingl@...glemail.com> wrote:
>
>> Codec driver can implement .hw_params and/or .prepare from struct
>> snd_soc_dai_ops. For codec-to-codec links only the former (.hw_params)
>> callback has been called.
>>
>> On platforms like Amlogic Meson8/8b/8m2 the SoC's sound card
>> (sound/soc/meson/gx-card.c) uses a codec-to-codec link for the HDMI
>> codec output because further digital routing is required after the
>> backend. The new DRM HDMI (audio) codec framework (which internally
>> uses sound/soc/codecs/hdmi-codec.c) relies on the .prepare callback
>> of the hdmi-codec to be called. Implement a call to
>> snd_soc_dai_prepare() so the .prepare callback of the hdmi-codec is
>> called on those platforms.
>>
>> For platforms or sound cards without a codec-to-codec link with
>> additional parameters (which applies to most hardware) this changes
>> nothing as the .prepare callback is already called via
>> snd_pcm_do_prepare() (as well as dpcm_fe_dai_prepare() and
>> dpcm_be_dai_prepare()) on those.
>>
>> Suggested-by: Jerome Brunet <jbrunet@...libre.com>
>> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
>
> Thanks for working on this. Overall it looks good.
>
> Not sure if the call the .prepare() should go at the beginning of
> POST_PMU, as done here, or at the end of PRE_PMU ? 
>
>> ---
>>  sound/soc/soc-dapm.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/sound/soc/soc-dapm.c b/sound/soc/soc-dapm.c
>> index 99521c784a9b..ac8eef217dc4 100644
>> --- a/sound/soc/soc-dapm.c
>> +++ b/sound/soc/soc-dapm.c
>> @@ -4013,6 +4013,13 @@ static int snd_soc_dai_link_event(struct snd_soc_dapm_widget *w,
>>  		break;
>>  
>>  	case SND_SOC_DAPM_POST_PMU:
>> +		snd_soc_dapm_widget_for_each_sink_path(w, path) {
>> +			sink = path->sink->priv;
>> +
>> +			snd_soc_dai_prepare(sink, substream);

I initially missed it but I think you should do that on the source path
too

On Amlogic, the cpu side of the link does not have a .prepare() callback
but it would be incorrect to do the codec side only if it did.

>> +			ret = 0;
>> +		}
>> +
>>  		snd_soc_dapm_widget_for_each_sink_path(w, path) {
>>  			sink = path->sink->priv;

-- 
Jerome