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Subject: Re: [RFC PATCH v2 5/5] ASoC: apple: Add macaudio machine driver
From:   =?utf-8?Q?Martin_Povi=C5=A1er?= <povik+lin@cutebit.org>
In-Reply-To: <YqIOwrRN8rPUF7Y8@sirena.org.uk>
Date:   Thu, 9 Jun 2022 17:27:12 +0200
Cc:     Liam Girdwood <lgirdwood@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzk+dt@kernel.org>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>, alsa-devel@alsa-project.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mark Kettenis <kettenis@openbsd.org>,
        Hector Martin <marcan@marcan.st>,
        Sven Peter <sven@svenpeter.dev>, asahi@lists.linux.dev
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Message-Id: <7F1B2324-4376-4776-BA6D-FBC8892F10C2@cutebit.org>
References: <20220606191910.16580-1-povik+lin@cutebit.org>
 <20220606191910.16580-6-povik+lin@cutebit.org>
 <YqH2uCgaedf0HQPE@sirena.org.uk>
 <8961DDD2-93FF-4A18-BCA2-90FCE298F517@cutebit.org>
 <YqIOwrRN8rPUF7Y8@sirena.org.uk>
To:     Mark Brown <broonie@kernel.org>
Precedence: bulk


> On 9. 6. 2022, at 17:16, Mark Brown <broonie@kernel.org> wrote:
>=20
> On Thu, Jun 09, 2022 at 04:09:57PM +0200, Martin Povi=C5=A1er wrote:
>>> On 9. 6. 2022, at 15:33, Mark Brown <broonie@kernel.org> wrote:
>=20
>>>> +		/*
>>>> +		 * Primary FE
>>>> +		 *
>>>> +		 * The mclk/fs ratio at 64 for the primary frontend is =
important
>>>> +		 * to ensure that the headphones codec's idea of left =
and right
>>>> +		 * in a stereo stream over I2S fits in nicely with =
everyone else's.
>>>> +		 * (This is until the headphones codec's driver supports
>>>> +		 * set_tdm_slot.)
>>>> +		 *
>>>> +		 * The low mclk/fs ratio precludes transmitting more =
than two
>>>> +		 * channels over I2S, but that's okay since there is the =
secondary
>>>> +		 * FE for speaker arrays anyway.
>>>> +		 */
>>>> +		.mclk_fs =3D 64,
>>>> +	},
>=20
>>> This seems weird - it looks like it's confusing MCLK and the bit =
clock
>>> for the audio bus.  These are two different clocks.  Note that it's =
very
>>> common for devices to require a higher MCLK/fs ratio to deliver the =
best
>>> audio performance, 256fs is standard.
>=20
>> On these machines we are not producing any other clock for the codecs
>> besides the bit clock, so I am using MCLK interchangeably for it. (It =
is
>> what the sample rate is derived from after all.)
>=20
> Please don't do this, you're just making everything needlessly hard to
> understand by using standard terminology inappropriately and there's a
> risk of breakage further down the line with drivers implementing the
> standard ops.

OK

>> One of the codec drivers this is to be used with (cs42l42) expects to =
be
>> given the I2S bit clock with
>=20
>>  snd_soc_dai_set_sysclk(dai, 0, mclk, SND_SOC_CLOCK_IN);
>=20
> That's very, very non-standard...
>=20
>> I can rename mclk to bclk in all of the code to make it clearer =
maybe.
>> Also the platform driver can take the bit clock value from =
set_bclk_ratio,
>> instead of set_sysclk from where it takes it now. The cs42l42 driver =
I can
>> patch too to accept set_bclk_ratio.
>=20
> ...indeed, set_bclk_ratio() is a better interface for setting the bclk
> ratio - the CODEC driver should really be doing that as well.

OK, adding that to my TODOs.

>>> This shouldn't be open coded in a driver, please factor it out into =
the
>>> core so we've got an API for "set limit X on control Y" then call =
that.
>=20
>> There=E2=80=99s already snd_soc_limit_volume, but it takes a fixed =
control name.
>> Can I extend it to understand patterns beginning with a wildcard, =
like
>> '* Amp Gain Volume=E2=80=99?
>=20
> Or add a new call that does that.

OK