linux-kernel - Re: [PATCH v4 00/17] ALSA: hda: cirrus: Add initial DSP support and firmware loading

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Date:   Mon, 30 May 2022 09:08:46 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Takashi Iwai <tiwai@...e.de>
CC:     Vitaly Rodionov <vitalyr@...nsource.cirrus.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, Mark Brown <broonie@...nel.org>,
        <alsa-devel@...a-project.org>, <patches@...nsource.cirrus.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 00/17] ALSA: hda: cirrus: Add initial DSP support and
 firmware loading

On Fri, May 27, 2022 at 06:13:38PM +0200, Takashi Iwai wrote:
> On Wed, 25 May 2022 15:16:21 +0200,
> Vitaly Rodionov wrote:
> The idea to add / delete controls by the control element change
> doesn't sound good; as already mentioned in my reply to the previous
> patch set, the change of the control elements can be triggered too
> easily by any normal users who have the access to the sound devices.
> It means thousands of additions and removals per second could be
> attacked by any user.
> 

This I am a little less sure how we handle. I mean arn't there
already a few ways to do this? Both the existing ASoC wm_adsp
stuff, and the topology stuff (used on all new Intel platforms,
so very widely deployed) let you create controls by loading a
firmware file. Also within ALSA itself can't user-space create
user ALSA controls? Is there some rate limiting on that? How is
this issue tackled there?

> Moreover, the new controls with TLV controls don't look following the
> standard TLV syntax (type-length-value).  My previous questions about
> the TLV usages are still unanswered, so I'm not sure what impact this
> would have, though.  At least, alsactl behavior must be checked
> beforehand. If this is really device-specific (non-)TLV usages, it has
> to be clearly documented.
> 

The TLV stuff should be completely removed once my latest
comments have been updated. I don't think we need this for the
amps and I would also rather keep the usage to a minimum until
one of us finally gets around to resolving the large control
issues in a way that is more acceptable to everyone (likely
with a new IOCTL).

Thanks,
Charles