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Date: Tue, 24 Apr 2018 23:13:47 +0200 From: Lukas Wunner <lukas@...ner.de> To: Kai Heng Feng <kai.heng.feng@...onical.com> Cc: Pali Rohár <pali.rohar@...il.com>, Takashi Iwai <tiwai@...e.de>, mjg59@...f.ucam.org, dvhart@...radead.org, andy@...radead.org, Mario Limonciello <mario.limonciello@...l.com>, alsa-devel@...a-project.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, platform-driver-x86@...r.kernel.org Subject: Re: [alsa-devel] [PATCH v4 3/3] ALSA: hda: Disabled unused audio controller for Dell platforms with Switchable Graphics On Mon, Apr 23, 2018 at 04:18:35PM +0800, Kai Heng Feng wrote: > >On Apr 23, 2018, at 4:08 PM, Pali Rohár <pali.rohar@...il.com> wrote: > >On Monday 23 April 2018 16:04:55 Kai Heng Feng wrote: > >>>On Apr 20, 2018, at 8:10 PM, Takashi Iwai <tiwai@...e.de> wrote: > >>>On Fri, 20 Apr 2018 11:44:32 +0200, Kai-Heng Feng wrote: > >>>>Now it's a typical discrete-only system. HDMI audio comes from AMD audio > >>>>controller, others from Intel audio controller. > >>>> > >>>>When SG is enabled, the unused AMD audio contoller still exposes its > >>>>sysfs, so userspace still opens the control file and stream. If > >>>>userspace tries to output sound through the stream, it hangs the system. > >>> > >>>Hm, could you give more information about how it hangs? > >> > >>Well, I should say "it hangs the userspace process" instead. > >> > >>$ speaker-test -t wav -c 2 -D hw:CARD=HDMI,DEV=3 > >>...and it just stopped. Can't Ctrl+C to break it. > > > >So userspace process cannot be killed at all? Then it is different bug > >in kernel and disabling pci device is just a workaround. Not a real fix. > > > >I would propose to find out what happen and why it cannot be killed > >(probably it stuck somewhere in kernel) and fix it properly. > > That's because the audio device got runtime suspended by the graphics. > > In this case, if we really want to use the the discrete audio, then we also > need to wake up the graphics. > The discrete audio is totally useless when SG is enabled, so my approach is > just to disable it. I don't quite follow, that should be fixed by commit 07f4f97d7b4b ("vga_switcheroo: Use device link for HDA controller") which landed in v4.17-rc1. My understanding was that with SG enabled, the external DP/HDMI ports are muxed to the Intel GPU, so audio can only be streamed to external displays by the Intel HDA, not by the HDA integrated into the discrete AMD/Nvidia GPU. Audio streamed to the latter would essentially end up in a blackhole. And preventing the user from seeing such useless audio devices was the sole purpose of this commit. Am I missing something? Thanks, Lukas
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