On Sat, 29 Apr 2017 19:00:28 +0200, Tanu Kaskinen wrote: > > On Sat, 2017-04-29 at 17:42 +0200, Takashi Iwai wrote: > > On Sat, 29 Apr 2017 14:45:41 +0200, > > Arun Raghavan wrote: > > > > > > (looping in Takashi for his thoughts, since we'd discussed this a long > > > time ago) > > > > > > On Fri, 28 Apr 2017, at 12:38 AM, Tanu Kaskinen wrote: > > > > On Wed, 2017-04-26 at 14:19 +0530, Arun Raghavan wrote: > > > > > On Mon, 24 Apr 2017, at 08:36 PM, Tanu Kaskinen wrote: > > > > > > Previously, if front:x didn't work, we would try to use hw:x for analog > > > > > > stereo output. There's no guarantee that hw:x is an analog output, > > > > > > however. For example, the Intel HDMI LPE driver uses hw:x for HDMI > > > > > > output, and PulseAudio incorrectly created analog profiles for that > > > > > > card, because front:x doesn't work but hw:x does. > > > > > > > > > > > > This patch changes things so that the analog stereo mapping doesn't any > > > > > > more use hw:x as a fallback. A separate "unknown stereo" fallback > > > > > > mapping is added to handle the rare case where hw:x is the only PCM > > > > > > device that works. > > > > > > > > > > > > BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=100488 > > > > > > --- > > > > > > > > > > I recall that front: actually adds a softvol on top of hw: (in some > > > > > cases?), and we actually wanted to move to hw: always. > > > > > > > > Using hw: always seems like a bad idea (for the reasons described in > > > > this patch). > > > > > > > > > Do we know if that's still true? > > > > > > > > At least I don't know. > > > > The softvol is skipped by passing SND_PCM_NO_SOFTVOL bit flag at > > opening a stream even if softvol is included in the configuration. > > IIRC, this was introduced exactly for PA :) > > I looked at some old discussions[1][2] to find out why we're still not > using the NO_SOFTVOL flag. The problem seems to be that using the flag > isn't enough to guarantee that there aren't any softvol elements in the > mixer. It seems that if any program ever has used "front:" without the > NO_SOFTVOL flag, the softvol PCM element will be created and will > remain forever on that system. If the mixer element has been created > once, then starting to use NO_SOFTVOL causes a regression, because > PulseAudio will see and use the PCM mixer element, but the mixer > element won't be hooked to the actual softvol plugin. That is, the > mixer element won't have any effect on the volume. > > In [1] Takashi says that PulseAudio can check if the PCM element is > user-created, but in [2] Jaroslav says that it's not possible. It is still possible to differentiate: the "PCM" volume is with SND_CTL_ELEM_ACCESS_USER in its access bits when created by softvol, while the one from the kernel driver is without that. I guess the issue Jaroslav mentioned is that you cannot judge in 100% whether it is from the softvol. It might be that user created for a different purpose. But, in either ways, PA doesn't want to care about such a volume element, so it'd be safe to say that as default PA should skip the user-element. The only useful case to allow user-element would be to deal with the faked card, e.g. via aloop and pass-through all ctls via user ctls. But such a card won't be detected properly by PA in anyway. So, although it'd be still required to allow the user-space elements, it may be optional, e.g. enabled only by some options. Takashi > I didn't see anyone suggesting using "hw:" instead of "front:", and I > don't see how that would help anyway. Arun, do you think this patch is > ok to be applied? > > [1] http://mailman.alsa-project.org/pipermail/alsa-devel/2010-August/031184.html > [2] https://lists.freedesktop.org/archives/pulseaudio-discuss/2013-May/017313.html > > -- > Tanu > > https://www.patreon.com/tanuk >
