Re: [alsa-devel] [PATCH v4 3/3] ALSA: hda: Disabled unused audio controller for Dell platforms with Switchable Graphics

From: Kai Heng Feng
Date: Mon Apr 23 2018 - 04:18:57 EST

On Apr 23, 2018, at 4:08 PM, Pali RohÃr <pali.rohar@xxxxxxxxx> wrote:

On Monday 23 April 2018 16:04:55 Kai Heng Feng wrote:
On Apr 20, 2018, at 8:10 PM, Takashi Iwai <tiwai@xxxxxxx> 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.


@@ -1627,6 +1629,42 @@ static void check_msi(struct azx *chip)


This should be IS_REACHABLE(), as both dell-laptop and HD-audio are

Thanks, will update in next version.

+static bool check_dell_switchable_gfx(struct pci_dev *pdev)

I'd remove "_dell" word here. Such a check would be likely needed for
other vendors, and it's quite possible that the function will be
extended to cover a wider DMI table.

Makes sense. Will also update this one.




Pali RohÃr