linux-kernel - Re: [PATCH] ALSA: core: Remove trigger_tstamp

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Message-ID: <c2a46079-b9fa-46fb-8d2d-e01e5d620ea7@mailbox.org>
Date: Tue, 13 Aug 2024 14:54:42 +0200
From: Zeno Endemann <zeno.endemann@...lbox.org>
To: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
 linux-sound@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
 Cezary Rojewski <cezary.rojewski@...el.com>,
 Christian Brauner <brauner@...nel.org>, Mark Brown <broonie@...nel.org>,
 Pavel Hofman <pavel.hofman@...tera.com>, David Howells
 <dhowells@...hat.com>, Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
 Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
 Bard Liao <yung-chuan.liao@...ux.intel.com>,
 Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
 Kai Vehmanen <kai.vehmanen@...ux.intel.com>
Subject: Re: [PATCH] ALSA: core: Remove trigger_tstamp_latched

Pierre-Louis Bossart wrote on 13.08.24 10:04:
> by focusing on the trigger timestamp I think you're looking at the wrong
> side of the problem. The timestamping is improved by using the same
> hardware counter for the trigger AND regular timestamp during
> playback/capture. If you look at a hardware counter during
> playback/capture but the start position is recorded with another method,
> would you agree that there's a systematic non-reproducible offset at
> each run? You want the trigger and regular timestamps to be measured in
> the same way to avoid measurement differences.

I am not sure what you are talking about. I have not seen any place in the
code where the trigger timestamp is taken in any other more sophisticated
way than what the default is doing, i.e. calling snd_pcm_gettime. So I do
not see how your custom *trigger* timestamps are done "with another method".

> I will not disagree that most applications do not need precise
> timestamping, but if you want to try to enable time-of-flight
> measurements for presence or gesture detection you will need higher
> sampling rates and micro-second level accuracy.

I don't know, this sounds very theoretical at best to me. However I do not
have the desire to try to further argue and convince you otherwise.

Do you want to propose a different solution for the stop trigger timestamp
bug? That is my main goal after all.