linux-kernel - Re: [PATCH 3/3] soundwire: bus: Fix lost UNATTACH when re-enumerating

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Message-ID: <b163327f-587d-d933-35de-7058cdcd6b9e@opensource.cirrus.com>
Date:   Mon, 29 Aug 2022 10:50:34 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        <vkoul@...nel.org>, <yung-chuan.liao@...ux.intel.com>,
        <sanyog.r.kale@...el.com>
CC:     <patches@...nsource.cirrus.com>, <alsa-devel@...a-project.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] soundwire: bus: Fix lost UNATTACH when re-enumerating

On 26/08/2022 09:06, Pierre-Louis Bossart wrote:
> 
<SNIP>
> 
> Thanks for the detailed answer, this sequence of events will certainly
> defeat the Cadence IP and the way sticky bits were handled.
> 
> The UNATTACHED case was assumed to be a really rare case of losing sync,
> i.e. a SOFT_RESET in SoundWire parlance.
> 
> If you explicitly do a device reset, that would be a new scenario that
> was not considered before on any of the existing SoundWire commercial
> devices. It's however something we need to support, and your work here
> is much appreciated.
> 
> I still think we should re-check the actual status from a PING frame, in
> order to work with more current data than the sticky bits taken at an
> earlier time, but that would only be a minor improvement.
> 
> I also have a vague feeling that additional work is needed to make sure
> the DAIs are not used before that second enumeration and all firmware
> download complete. I did a couple of tests last year where I used the
> debugfs interface to issue a device reset command while streaming audio,
> and the detach/reattach was not handled at the ASoC level.
> 
> I really don't see any logical flaws in your patch as is, so
> 
> Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> 

I have pushed an alternative fix that waits until it sees an UNATTACHED
status before reprogramming the device ID.
https://lore.kernel.org/lkml/20220829094458.1169504-1-rf@opensource.cirrus.com/T/#t

I've tested it with 4 amps on the same bus, all being reset after their
firmware has been downloaded.

I leave it to you to choose which fix you prefer. The second fix is
simpler and I didn't see any problems in testing.