At Wed, 15 May 2013 13:22:03 +0200, Jaroslav Kysela wrote: > > Date 15.5.2013 13:03, David Henningsson wrote: > > On 05/15/2013 12:53 PM, Jaroslav Kysela wrote: > >> Date 15.5.2013 12:48, Takashi Iwai wrote: > >>> At Wed, 15 May 2013 12:26:51 +0200, > >>> Jaroslav Kysela wrote: > >>>> > >>>> Date 15.5.2013 11:55, Arun Raghavan wrote: > >>>>> Hello, > >>>>> A number of users have intermittently(?) been hitting a crash in > >>>>> alsa-lib 1.0.27 [1, 2] related to the softvol plugin. I'm not able to > >>>>> reproduce this reliably, so can't find an easy way to debug/fix. > >>>> > >>>> The problem is that the offsets are not in sync in this case [1]: > >>>> > >>>> src_offset = 38560 > >>>> dst_offset = 38568 > >>>> frames = 16374 > >>>> > >>>> Could you reproduce this bug in any way? At least snd_pcm_dump() before > >>>> the failing snd_pcm_mmap_commit() call might help to determine what was > >>>> the status before the assert() was entered. > >>> > >>> Yep. And this path is actually with volume 0dB, that is, a simply > >>> passthrough in softvol. Thus the bug may hit essentially any > >>> plugins, not specifically softvol. > >>> > >>> > >>>>> However, this raises a tangential question - why do we need softvol to > >>>>> be plugged for 'front' at all? David explained to me that this is to > >>>>> guarantee the existence of a PCM control. Perhaps I don't fully > >>>>> understand this, because I'm unconvinced by the reason. Could someone > >>>>> explain/refute? > >>>>> > >>>>> This is especially bad for us, from PulseAudio's perspective, because we > >>>>> aren't getting a zero-copy path. > >>>> > >>>> If the softvol is set to 0dB (no attenuation or gain), then the ring > >>>> buffer pointers are moved without any sample processing, so the > >>>> zero-copy functionality is kept. > >>> > >>> Yeah, a sort of. The mmap is cleared in the slave PCM, so actually > >>> there will be copy operations in underlying layers even though softvol > >>> itself does zero copy. > >>> > >>> Actually it makes no sense to keep softvol for PA, but the problem is > >>> always the regression. There are certainly users without PA, which > >>> might still rely on the softvol for such hardware without the amp > >>> control. > >>> > >>> Maybe We can add some flag to indicate whether to handle softvol or > >>> not, e.g. defaults.pcm.skip_softvol, and let PA set this in its config > >>> space. Setting a config item itself would break anything, so it'll > >>> still work with old alsa-lib (but with softvol). > >> > >> We have already SND_PCM_NO_SOFTVOL open mode for this purpose, so I > >> wonder, why PA does not use it.. > > > > The problem is knowing whether PCM is a softvol or not. In some cases, > > we need to set PCM to control hardware volume. > > > > Maybe, if we could figure this out somehow, we could ignore the PCM > > mixer control (or possibly set it to zero) in case PCM is a softvol, > > and actually use it if PCM is not a softvol. > > > > It does not look like this is currently possible from the simple mixer > > interface, but I might be missing something? > > It is not possible. Perhaps, we may create a new dummy mixer control (in > an inactive state) which will identify the presence of the softvol > plugin, like: > > "Softvol PCM Playback Volume" - full name for the raw control API > "Softvol PCM" - simple mixer name Well, if changing in such a way, I'd rather drop softvol from HDA-Intel.conf. If we could give some flag in mixer API, we could add a code to filter out the user controls from the mixer's hctl. But snd_mixer_attach() takes only the string, and the string modifier may lead to the incompatibility when used with an older version. Hmm. Takashi
