On Thu, Mar 08, 2018 at 06:38:45PM +0800, Kai Heng Feng wrote: > >On Mar 8, 2018, at 5:38 PM, Lukas Wunner <lukas@xxxxxxxxx> wrote: > >On Thu, Mar 08, 2018 at 05:10:23PM +0800, Kai-Heng Feng wrote: > >>Some Dell platforms (Preicsion 7510/7710/7520/7720) have a BIOS option > >>"Switchable Graphics" (SG). > >> > >>When SG is enabled, we have: > >>00:02.0 VGA compatible controller: Intel Corporation Device 591b (rev 04) > >>00:1f.3 Audio device: Intel Corporation CM238 HD Audio Controller (rev 31) > >>01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. > >>[AMD/ATI] Ellesmere [Polaris10] > >>01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere > >>[Radeon RX 580] > >> > >>The Intel Audio outputs all the sound, including HDMI audio. The audio > >>controller comes with AMD graphics doesn't get used. > >> > >>When SG is disabled, we have: > >>00:1f.3 Audio device: Intel Corporation CM238 HD Audio Controller (rev 31) > >>01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. > >>[AMD/ATI] Ellesmere [Polaris10] > >>01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere > >>[Radeon RX 580] > >> > >>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 controller still exposes its > >>sysfs, so userspace still opens the control file and stream. If > >>userspace tries to output sound through the stream, it hangs when > >>runtime suspend kicks in: > >>[ 12.796265] snd_hda_intel 0000:01:00.1: Disabling via vga_switcheroo > >>[ 12.796367] snd_hda_intel 0000:01:00.1: Cannot lock devices! > > > >This should be fixed by the following series: > >https://lists.freedesktop.org/archives/dri-devel/2018-March/168012.html > > > >Please verify that by testing the series on the machine in question. > >I'm hoping to get those patches in for 4.17. I suspect that your > >patch may not be necessary then. > > I no longer see the warning message with your patch. Thanks! Awesome, thanks for testing! > >>Since the discrete audio controller isn't useful when SG enabled, we > >>should just disable the device. > > > >I don't quite follow, when SG is enabled but hda_intel doesn't bind > >to the AMD audio device, how are you going to stream audio to > >external displays? Are external DP/HDMI ports muxed to the integrated > >GPU when SG is enabled? > > Yes. It's a muxed port. > The can directly output via integrated Intel GPU when SG is enabled. > The discrete audio controller never gets used when SG is enabled. Okay, that's a crucial piece of information which I think should be made more explicit in the commit message and probably also in a code comment so that someone reading through hda_intel.c doesn't have to look in the git history to understand what's going on. I'd remove the portion of the commit message pertaining to runtime suspend and instead write something like: If Switchable Graphics is enabled, external DP/HDMI ports are muxed to the Intel GPU and HDA controller and therefore those on the AMD HDA controller shouldn't be exposed to user space. Thanks, Lukas
