Re: [PATCH] ALSA: hda: intel: Fix Optimus when GPU has no sound

[Maxim Mikityanskiy <maxtram95@xxxxxxxxx>]

On Thu, 05 Sep 2024 at 16:24:26 +0200, Takashi Iwai wrote:
> On Wed, 04 Sep 2024 22:39:55 +0200,
> Maxim Mikityanskiy wrote:
> > 
> > Lenovo IdeaPad Z570 with NVIDIA GeForce Ge 520M doesn't have sound on

Spotted a typo: s/520M/540M/

> > the discrete GPU. snd_hda_intel probes the device and schedules
> > azx_probe_continue(), which fails at azx_first_init(). The driver ends
> > up probed, but calls azx_free() and stops the chip. However, from the
> > runtime PM point of view, the device remains active, because the PCI
> > subsystem makes it active on probe, and it's still bound. It prevents
> > vga_switcheroo from turning off the DGPU (pci_create_device_link() syncs
> > power management for the video and audio devices).
> > 
> > Fix it by forcing the device to the suspended state in azx_free().
> > 
> > Fixes: 07f4f97d7b4b ("vga_switcheroo: Use device link for HDA controller")
> > Signed-off-by: Maxim Mikityanskiy <maxtram95@xxxxxxxxx>
> 
> What if this device probe is skipped (e.g. adding your device entry to
> driver_denylist[] in hda_intel.c)?  Is the device also in the
> runtime-suspended state?

I added the following:

{ PCI_DEVICE_SUB(0x10de, 0x0bea, 0x0000, 0x0000) },

The probe was apparently skipped (the device is not attached to a
driver), runtime_status=suspended, runtime_usage=0, the GPU goes to
DynOff.

However, I'm not sure whether it's a good idea to blacklist 540M
entirely, as there might be other laptops with this GPU that have sound,
and AFAIK there are variants of Lenovo Z570 with other NVIDIA GPUs.

Another way to make vga_switcheroo work is to disable quirk_nvidia_hda,
although I don't know whether it can be done without recompiling the
kernel. In this case, 0000:01:00.1 doesn't even appear on the bus.

(Note that I need to set nouveau.modeset=2 either way, otherwise it
stays in DynPwr if the screen is on.)

> 
> 
> thanks,
> 
> Takashi
> 
> > ---
> >  sound/pci/hda/hda_intel.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
> > index b79020adce63..65fcb92e11c7 100644
> > --- a/sound/pci/hda/hda_intel.c
> > +++ b/sound/pci/hda/hda_intel.c
> > @@ -1361,8 +1361,20 @@ static void azx_free(struct azx *chip)
> >  	if (use_vga_switcheroo(hda)) {
> >  		if (chip->disabled && hda->probe_continued)
> >  			snd_hda_unlock_devices(&chip->bus);
> > -		if (hda->vga_switcheroo_registered)
> > +		if (hda->vga_switcheroo_registered) {
> >  			vga_switcheroo_unregister_client(chip->pci);
> > +
> > +			/* Some GPUs don't have sound, and azx_first_init fails,
> > +			 * leaving the device probed but non-functional. As long
> > +			 * as it's probed, the PCI subsystem keeps its runtime
> > +			 * PM status as active. Force it to suspended (as we
> > +			 * actually stop the chip) to allow GPU to suspend via
> > +			 * vga_switcheroo.
> > +			 */
> > +			pm_runtime_disable(&pci->dev);
> > +			pm_runtime_set_suspended(&pci->dev);
> > +			pm_runtime_enable(&pci->dev);
> > +		}
> >  	}
> >  
> >  	if (bus->chip_init) {
> > -- 
> > 2.46.0
> >