linux-kernel - Re: [linux-sunxi] Re: Audio sound card name [was [PATCH 4/7] arm64: dts: allwinner: a64: Add HDMI audio]

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Message-ID: <20200429120511.GG4201@sirena.org.uk>
Date:   Wed, 29 Apr 2020 13:05:11 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Maxime Ripard <maxime@...no.tech>, Chen-Yu Tsai <wens@...e.org>,
        Clément Péron <peron.clem@...il.com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Takashi Iwai <tiwai@...e.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Marcus Cooper <codekipper@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [linux-sunxi] Re: Audio sound card name [was [PATCH 4/7] arm64:
 dts: allwinner: a64: Add HDMI audio]

On Wed, Apr 29, 2020 at 11:43:06AM +0100, Robin Murphy wrote:
> On 2020-04-29 9:17 am, Maxime Ripard wrote:
> > On Wed, Apr 29, 2020 at 02:24:00PM +0800, Chen-Yu Tsai wrote:

Please delete unneeded context from mails when replying.  Doing this
makes it much easier to find your reply in the message, helping ensure
it won't be missed by people scrolling through the irrelevant quoted
material.

> > If we also end up with "HDMI" as our card name, then the userspace has no way to
> > tell anymore if it's running from an rk3328 or an allwinner SoC, or something
> > else entirely. And therefore it cannot really configure anything to work out of
> > the box anymore.

> OK, you're a userspace audio application - enlighten me as to what exact
> chip you're running on here, and why you need to know:

> card 0: HDMI [HDA ATI HDMI]

> or how about here?

> card 0: Intel [HDA Intel]

In the case of HDMI for embedded platforms since there is generally no
control in the audio path it is unlikely to make a *huge* difference,
though if there are expansion buses or multiple HDMI ports it can be
useful to help people identify which particular HDMI port it is.  For
other cards the names are part of userspace working out which config
file to apply to the card so deduplication can help, and also the
plastics tend to matter.

> With simple-audio-card we're talking about trivial interfaces that often
> don't expose any controls at all, so there's unlikely to be much
> 'configuration' for userspace to do beyond choosing which card to output to.

This is a reasonable assumption for HDMI but it is not at all a
reasonable assumption for simple-audio-card in general - just because
the links between the SoC and the external components are simple that
doesn't mean that any of those components are simple, and even if the
hardware is simple that does not mean that configuration is unimportant
- the difference between full scale output and appropriate headphone
volumes is for example *extremely* important.

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