From mboxrd@z Thu Jan  1 00:00:00 1970
From: Clemens Ladisch <clemens@ladisch.de>
Subject: Re: Master Plan on rewinding
Date: Tue, 09 Sep 2014 10:43:06 +0200
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To: "Alexander E. Patrakov" <patrakov@gmail.com>, ALSA Development Mailing List <alsa-devel@alsa-project.org>, Takashi Iwai <tiwai@suse.de>, David Henningsson <david.henningsson@canonical.com>, Takashi Sakamoto <o-takashi@sakamocchi.jp>
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Alexander E. Patrakov wrote:
> |---------|---------P----h----p---------|-a-------|---------|
>
> So, what should alsa-lib return for snd_pcm_avail() and snd_pcm_rewind()?
> The driver only knows that "P" is already used, can infer that "p" isn't
> used yet, and knows nothing about samples in the middle.

Indeed.  However, the DMA pointer moves asynchronously, so it is possible
that it has already moved beyond p when snd_pcm_rewindable() returns.
For the samples between P and p, the risk is larger than for those after
p, but p is not a boundary where the risk abruptly decreases.

It would make sense to report the pointer update granularity, but not
to adjust the return value of snd_pcm_avail/rewindable().


Regards,
Clemens