linux-kernel - Re: [PATCH 1/2] ASoC: max98363: add soundwire amplifier driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y/z6EB+0beX2Ji2h@sirena.org.uk>
Date:   Mon, 27 Feb 2023 18:44:32 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     “Ryan <ryan.lee.analog@...il.com>,
        lgirdwood@...il.com, perex@...ex.cz, tiwai@...e.com,
        krzysztof.kozlowski@...aro.org, rf@...nsource.cirrus.com,
        ckeepax@...nsource.cirrus.com, herve.codina@...tlin.com,
        wangweidong.a@...nic.com, james.schulman@...rus.com,
        ajye_huang@...pal.corp-partner.google.com, shumingf@...ltek.com,
        povik+lin@...ebit.org, flatmax@...tmax.com,
        linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
        robh+dt@...nel.org, devicetree@...r.kernel.org,
        ryans.lee@...log.com
Subject: Re: [PATCH 1/2] ASoC: max98363: add soundwire amplifier driver

On Mon, Feb 27, 2023 at 01:19:15PM -0500, Pierre-Louis Bossart wrote:
> On 2/27/23 12:47, Mark Brown wrote:
> > On Mon, Feb 27, 2023 at 10:17:45AM -0500, Pierre-Louis Bossart wrote:

> >> That seems wrong, why would you declare standard registers that are
> >> known to the bus and required to be implemented?

> > This is the register defaults table, it gets used to initialise the
> > register cache and optimise resync after suspend - all this does is
> > supply defaults for the cache.  That said...

> > I would suggest it's better to not supply defaults for ID registers and
> > read them back from the device otherwise things might get confused.

> The 'device_id' register is the good counter example: it includes a
> 'unique_id' field to deal with cases where there are identical devices
> on the same link. The unique_id is usually set with board-specific
> pin-strapping, so there's no good default value here. In previous Maxim
> 98373 amplifier configurations the unique IDs were 3 and 7 IIRC. The
> codec driver should not, rather shall not, assume any specific value here.

Yes, as I said above ID registers in particular are often better off
handled as volatile even ignoring any potential for them to show
variable configuration information.

> > ...if there's an issue with the SoundWire core modifying the registers
> > directly then the driver would need to mark all the core registers as
> > volatile so that they're not cached otherwise there will be collisions.
> > Or is it the case that we always need to go via the SoundWire core for
> > the generic registers, so they should just never be written at all?

> It's really that the SoundWire core will 'own' or take care of all
> 'standard' programming registers. There is no good reason for a codec
> driver to interfere with standard port programming or clock stop. The
> bus provides a set of callbacks that can be used for vendor-specific
> registers and sequences.

> Put differently, SoundWire codec drivers should only deal with
> non-standard vendor-specific registers.

OK, it'd be good to be clear about what the issue is when reviewing
things.  The registers *are* in the device's register map but the driver
shouldn't be referencing them at all and should instead be going via the
SoundWire core for anything in there.

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)