From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Henningsson Subject: Re: DP1.2 MST audio support discussion Date: Thu, 5 Nov 2015 10:07:03 +0100 Message-ID: <563B1C37.4010400@canonical.com> References: <96A12704CE18D347B625EE2D4A099D1974C250@SHSMSX103.ccr.corp.intel.com> <96A12704CE18D347B625EE2D4A099D1975281F@SHSMSX103.ccr.corp.intel.com> <56288783.1080503@canonical.com> <96A12704CE18D347B625EE2D4A099D19753A2D@SHSMSX103.ccr.corp.intel.com> <56288FF7.9030400@canonical.com> <96A12704CE18D347B625EE2D4A099D19753A91@SHSMSX103.ccr.corp.intel.com> <5628A3EB.8050306@canonical.com> <562A1237.2090909@canonical.com> <96A12704CE18D347B625EE2D4A099D19755BE7@SHSMSX103.ccr.corp.intel.com> <96A12704CE18D347B625EE2D4A099D197574CE@SHSMSX103.ccr.corp.intel.com> <563716D7.3000502@canonical.com> <96A12704CE18D347B625EE2D4A099D19765611@SHSMSX103.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from youngberry.canonical.com (youngberry.canonical.com [91.189.89.112]) by alsa0.perex.cz (Postfix) with ESMTP id 7E4C526531B for ; Thu, 5 Nov 2015 10:07:07 +0100 (CET) In-Reply-To: <96A12704CE18D347B625EE2D4A099D19765611@SHSMSX103.ccr.corp.intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: "Yang, Libin" , Takashi Iwai Cc: ALSA Development Mailing List , "airlied@linux.ie" , "Lin, Mengdong" , "Nikula, Jani" , "Girdwood, Liam R" , "Lu, Han" , Raymond Yau , "tanuk@iki.fi" List-Id: alsa-devel@alsa-project.org On 2015-11-04 15:17, Yang, Libin wrote: > + Jani, who is from Intel gfx team. > >> -----Original Message----- >> From: David Henningsson [mailto:david.henningsson@canonical.com] >> Sent: Monday, November 02, 2015 3:55 PM >> To: Yang, Libin; Takashi Iwai >> Cc: Lin, Mengdong; Raymond Yau; airlied@linux.ie; tanuk@iki.fi; ALSA >> Development Mailing List; Girdwood, Liam R; Lu, Han >> Subject: Re: [alsa-devel] DP1.2 MST audio support discussion >> >> >> >> On 2015-11-02 08:30, Yang, Libin wrote: >>> >>>>> 4. power management >>>>> If we close the PCM when disconnecting monitor, the driver will >>>> return >>>>> -ENODEV, and we assume user space will close the PCM at once . >>>> ... if we implement it. Actually this behavior (returning -ENODEV) is >>>> not mandatory and needs investigation beforehand, whether this >>>> breaks >>>> any applications, especially PA. >>> Yes. I heard that PA has dummy PCM and when there is no HW to >>> play the audio, PA can smoothly move the PCM from HW to dummy >>> PCM. If it's true, stopping PCM will not break PA, I think. >> >> Well, in most cases (not all) there will be an analog output available, >> so we're more likely to move there than to a dummy PCM. The >> problem is >> that PA does not currently figure out that a -ENODEV means that one >> should switch from a digital to an analog profile. So, at least at this >> point, don't expect a "smooth move". >> >> I'm not sure if this is a good idea or not, but just brainstorming here: >> >> If PA (or other application) tries to play back to a PCM, and that PCM >> is currently unassigned. What would happen if we actually assigned a >> converter node at that point, but no pin node connected to that >> converter node? Would that give a backwards compatible behaviour? I >> e, >> audio userspace could successfully play back audio through the >> converter >> node, but then the audio goes nowhere because there is no pin node >> assigned? > > GFX team hope us that if there is no monitor connected, audio > should release gfx so gfx driver can enter power save mode. > Based on the requirement, audio driver may need stop playback > as soon as the monitor is disconnected. I'm not talking about continuous playback here, so power consumption should not be a big concern. E g, if it takes a second or so before PA reroutes audio somewhere else, it's not a big deal from a power save perspective. So I'm asking my question again. What would happen (on Intel hardware), if you stream audio to a converter node on the audio codec, and there is no pin node connected to that converter node? -- David Henningsson, Canonical Ltd. https://launchpad.net/~diwic