linux-kernel - Re: [PATCH] ASoC: core: restore dpcm flags semantics

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Message-ID: <1ja6zg85xw.fsf@starbuckisacylon.baylibre.com>
Date:   Fri, 31 Jul 2020 10:06:03 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>
Cc:     alsa-devel@...a-project.org, Stephan Gerhold <stephan@...hold.net>,
        Kevin Hilman <khilman@...libre.com>,
        linux-kernel@...r.kernel.org, zhangn1985@...look.com,
        linux-amlogic@...ts.infradead.org
Subject: Re: [PATCH] ASoC: core: restore dpcm flags semantics


On Thu 30 Jul 2020 at 18:06, Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com> wrote:

> On 7/30/20 4:04 AM, Jerome Brunet wrote:
>>
>> On Wed 29 Jul 2020 at 17:56, Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com> wrote:
>>
>>> On 7/29/20 10:46 AM, Jerome Brunet wrote:
>>>> commit b73287f0b0745 ('ASoC: soc-pcm: dpcm: fix playback/capture checks')
>>>> changed dpcm_playback and dpcm_capture semantic by throwing an error if
>>>> these flags are not aligned with DAIs capabilities on the link.
>>>>
>>>> The former semantic did not force the flags and DAI caps to be aligned.
>>>> The flag previously allowed card drivers to disable a stream direction on
>>>> a link (whether or not such feature is deemed useful).
>>>>
>>>> With change ('ASoC: core: use less strict tests for dailink capabilities')
>>>> an error is thrown if the flags and and the DAI caps are not aligned. Those
>>>> parameters were not meant to aligned initially. No technical reason was
>>>> given about why cards should now be considered "broken" in such condition
>>>> is not met, or why it should be considered to be an improvement to enforce
>>>> that.
>>>>
>>>> Forcing the flags to be aligned with DAI caps just make the information
>>>> the flag carry redundant with DAI caps, breaking a few cards along the way.
>>>>
>>>> This change drops the added error conditions and restore the initial flag
>>>> semantics.
>>>
>>> or rather lack thereof.
>>
>> Again, why ? All there is so far is your personal preference. no facts.
>
> What would be the meaning/purpose of a dailink with .dpcm_capture set, with
> only dais that support playback only?
>
> What would be the meaning/purpose of a dailink with .capture_only set, but
> with a dai that supports playback?

You get to throw an error in those case

>
> What happens if none of these flags are set?

I think I already suggested to throw an error in the initial review of
your patch

>
> What happens when all these flags are set?

I don't see the problem here

>
> No one seems to know, so my suggestion is to align first on consistent
> configurations, then see what can be removed.
>
>>   * What we had gave capabilities to the link, independent of the DAI
>>     components. ASoC just computes the intersection of all that to
>>     determine which direction needs to be enabled. Seems rather simple
>>     and straight forward.
>
> that's what my last patch did, and when there is no intersection it
> complains. Please clarify what you expect when there is no overlap between
> dai and dailink capabilities. Keep in mind that we have a mix of hard-codec
> configuration and DT-created ones, your case is not the general one.
>
>>   * It worked for every user of DPCM so a far.
>
> Not completely true, when Morimoto-san added snd_soc_dai_stream_valid() it
> exposed tons of cases where the information on direction was not provided
> in a reliable at the DAI level. I will assert that we are still finding out
> cases with broken DAI configurations, and as a result we will also find
> broken dailink configurations. Your picture of DPCM as a perfectly
> functional system that I broke is a distortion of reality.

If it was not working, it was certainly not clear in the changelog.
What's clear is the regression it caused

>
> The reality is that we have to work in steps, first make sure all DAIs are
> properly described, then work on the dailinks and optimize at a later
> point. we will need warnings to find out what the problem cases are, and
> move slowly.

Sure, have it your way