[PATCH v2 3/3] ALSA: hda: allow direct complete with a powered-off GPU

[Andre Eikmeyer]

The HDA controller normally needs different WAKEEN settings for runtime and
system suspend, so azx_prepare() prevents direct complete. For a switcheroo
audio client whose bound GPU is already runtime suspended and switched off,
however, the controller is physically inaccessible and cannot signal wake
events.

Resuming the HDA function during system suspend also acquires its runtime
PM supplier. This powers the discrete GPU back on only to suspend it again
and can expose failures while restoring an otherwise unused GPU.

Direct complete is now allowed when the bound VGA device is both runtime
suspended and reported off by vga_switcheroo. Active GPUs and HDA
controllers without a switcheroo binding retain the existing WAKEEN
transition.

This was tested as part of the MacBookPro15,1 hybrid graphics series on
both the 2018 and 2019 revisions. The discrete GPU remains powered off
across system suspend when it is unused, and suspend and resume complete
successfully.

Signed-off-by: Andre Eikmeyer <dev@deq.rocks>
---
Changes in v2:
- Move the SUPPORT_VGA_SWITCHEROO guard to the sole call site.
- Explain the significance of the positive azx_prepare() return value.

 sound/hda/controllers/intel.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/sound/hda/controllers/intel.c b/sound/hda/controllers/intel.c
index 28c55c5..9132907 100644
--- a/sound/hda/controllers/intel.c
+++ b/sound/hda/controllers/intel.c
@@ -334,6 +334,7 @@ enum {
 #ifdef SUPPORT_VGA_SWITCHEROO
 #define use_vga_switcheroo(chip)	((chip)->use_vga_switcheroo)
 #define needs_eld_notify_link(chip)	((chip)->bus.keep_power)
+static struct pci_dev *get_bound_vga(struct pci_dev *pci);
 #else
 #define use_vga_switcheroo(chip)	0
 #define needs_eld_notify_link(chip)	false
@@ -1016,6 +1017,26 @@ static void __azx_runtime_resume(struct azx *chip)
 		display_power(chip, false);
 }
 
+#ifdef SUPPORT_VGA_SWITCHEROO
+static bool azx_vga_is_powered_off(struct azx *chip)
+{
+	struct pci_dev *pci;
+	bool powered_off = false;
+
+	if (!use_vga_switcheroo(container_of(chip, struct hda_intel, chip)))
+		return false;
+
+	pci = get_bound_vga(chip->pci);
+	if (pci) {
+		powered_off = pm_runtime_suspended(&pci->dev) &&
+			vga_switcheroo_get_client_state(pci) == VGA_SWITCHEROO_OFF;
+		pci_dev_put(pci);
+	}
+
+	return powered_off;
+}
+#endif
+
 static int azx_prepare(struct device *dev)
 {
 	struct snd_card *card = dev_get_drvdata(dev);
@@ -1025,6 +1046,12 @@ static int azx_prepare(struct device *dev)
 		return 0;
 
 	chip = card->private_data;
+#ifdef SUPPORT_VGA_SWITCHEROO
+	/* A positive return allows the PM core to use direct complete. */
+	if (azx_vga_is_powered_off(chip))
+		return 1;
+#endif
+
 	chip->pm_prepared = 1;
 	snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
 
@@ -1183,8 +1210,6 @@ static const struct dev_pm_ops azx_pm = {
 static int azx_probe_continue(struct azx *chip);
 
 #ifdef SUPPORT_VGA_SWITCHEROO
-static struct pci_dev *get_bound_vga(struct pci_dev *pci);
-
 static void azx_vs_set_state(struct pci_dev *pci,
 			     enum vga_switcheroo_state state)
 {
-- 
2.55.0