linux-kernel - Re: [PATCH 5/9] ASoC: ssm2602: Add workaround for playback with external MCLK

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Date:   Tue, 25 Apr 2023 17:42:03 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Paweł Anikiel <pan@...ihalf.com>
Cc:     alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, lgirdwood@...il.com, perex@...ex.cz,
        tiwai@...e.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, dinguyen@...nel.org,
        lars@...afoo.de, nuno.sa@...log.com, upstream@...ihalf.com
Subject: Re: [PATCH 5/9] ASoC: ssm2602: Add workaround for playback with
 external MCLK

On Tue, Apr 25, 2023 at 06:02:20PM +0200, Paweł Anikiel wrote:
> On Fri, Apr 14, 2023 at 7:35 PM Mark Brown <broonie@...nel.org> wrote:
> > On Fri, Apr 14, 2023 at 04:01:59PM +0200, Paweł Anikiel wrote:

> > > Apply a workaround for what seems to be a hardware quirk: when using
> > > an external MCLK signal, powering on Output and DAC for the first time
> > > produces output distortions unless they're powered together with whole
> > > chip power.

> > This doesn't seem coherent, these are multiple register writes so
> > clearly can't be done at the same moment as initial power on.  Clearly
> > there's some other constraint here.

> The "at the same time" part is done by writing multiple bits at once
> to SSM2602_PWR. But before that, SSM2602_ACTIVE has to be set, and
> then the chip is reset (SSM2602_RESET) to power everything down again.

So you need to power up the chip then do a register write sequence -
that's noticably different to what the description says.

> > > Here are some sequences run at the very start before a sw reset (and
> > > later using one of the NOT OK sequences from above):

> > >   ssmset 0x09 0x01 # core
> > >   ssmset 0x06 0x07 # chip, out, dac
> > >   OK

> > I can't tell what any of this is trying to say, especially given all the
> > magic numbers, and obviously no actual use of the driver should be
> > writing directly to the register map.

> These are shell commands run from userspace (with no ssm2602 driver
> present in the kernel). ssmset is a wrapper for the i2cset command:
> ssmset() {
>         i2cset -y 0 0x1a $(($1*2)) $2
> }
> I definitely should have made that more clear.

> Do you think these logs are worth adding? If so, I'll improve the
> explanation what these mean.

Probably?  Since I couldn't really follow what these were trying to tell
me it's a bit hard to say.  It looks like you worked this out yourself
rather than using an erratum so documenting where the workaround comes
from seems useful.

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