On Mar 8, 2018, at 7:30 PM, Lukas Wunner <lukas@xxxxxxxxx> wrote:
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.
I'll add the explanation to both comment and commit log.
Thanks for all the info.
Kai-Heng
Thanks,
Lukas
