linux-kernel - Re: [RFC PATCH 0/5] Apple Macs machine-level ASoC driver

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Date:   Thu, 31 Mar 2022 15:33:58 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Hector Martin <marcan@...can.st>
Cc:     Martin Povišer <povik+lin@...ebit.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Kettenis <kettenis@...nbsd.org>,
        Sven Peter <sven@...npeter.dev>
Subject: Re: [RFC PATCH 0/5] Apple Macs machine-level ASoC driver

On Thu, Mar 31, 2022 at 10:28:56PM +0900, Hector Martin wrote:

> The problem with this model is that, in particular in the case of
> speaker amps, incorrect settings can cause your speakers to blow up.
> This has been a longstanding problem with ASoC platforms (I should know,
> I *melted* the speakers in a Chromebook by toggling the wrong alsamixer
> control once, it even warped the external case, all without making any
> audible noise).

Yes, that's why we have platform_max - it was added for use with
Chromebooks originally, someone else had the same idea you did.  It's
used less often than I'd like since most embedded systems and even
things like Chromebooks have a software model where the actual sound
card isn't accessible to normal users but that's not the case once you
try to run a general purpose distro on there.

> kiosk-style software with no user control. It is completely unsuitable
> for a desktop Linux system, since it means users *will* destroy their
> hardware accidentally. So, some way or another, whatever is exposed has
> to be sanitized so that it can't go outside the envelope of what is safe
> for the hardware design. That cannot be known at the level of codec
> chips and speaker amp chips; it requires platform integration knowledge.

Yes, we should be trying to exclude configurations that could be
physically destructive but that's not what had been articulated and like
I said in reply to his last mail it's really not clear to me that what's
being proposed would actually accomplish the intended goal.  Targeted
restrictions that protect the system are fine and good, random "why
would anyone want this?" or "this is how you accomplish use case X" ones
are not since we do get users turning up with new ideas.

This is one reason why it's important to articulate what the intended
goal of changes is, what you've written above is perfectly fine and
reasonable but there was nothing about this in the original changelogs,
just statements about how silly it would be to configure these controls.

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