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

[Maxim Mikityanskiy <maxtram95@gmail.com>]

Lenovo IdeaPad Z570 with NVIDIA GeForce Ge 520M doesn't have sound on
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@gmail.com>
---
 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