Re: [PATCH] ALSA: pcm: fix wait_time calculations

[Takashi Iwai <tiwai@suse.de>]

On Wed, 05 Apr 2023 22:12:19 +0200,
Oswald Buddenhagen wrote:
> 
> ... in wait_for_avail() and snd_pcm_drain().
> 
> t was calculated in seconds, so it would be pretty much always zero, to
> be subsequently de-facto ignored due to being max(t, 10)'d. And then it
> (i.e., 10) would be treated as secs, which doesn't seem right.
> 
> However, fixing it to properly calculate msecs would potentially cause
> timeouts when using twice the period size for the default timeout (which
> seems reasonable to me), so instead use the buffer size plus 10 percent
> to be on the safe side ... but that still seems insufficient, presumably
> because the hardware typically needs a moment to fire up. To compensate
> for this, we up the minimal timeout to 100ms, which is still two orders
> of magnitude less than the bogus minimum.
> 
> substream->wait_time was also misinterpreted as jiffies, despite being
> documented as being in msecs. Only the soc/sof driver sets it - to 500,
> which looks very much like msecs were intended.
> 
> Speaking of which, shouldn't snd_pcm_drain() also use substream->
> wait_time?

Yes, and unifying the code might make more sense.

> As a drive-by, make the debug messages on timeout less confusing.
> 
> Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

I applied this patch as is now to for-next branch.


thanks,

Takashi