[alsa-devel] [PATCH] ALSA: hda - Force polling mode on CFL for fixing codec communication

[Takashi Iwai]

We've observed too long probe time with Coffee Lake machines, and the
likely cause is some communication problem between the HD-audio
controller and the codec chips.  While the controller expects an IRQ
wakeup for each codec response, it seems sometimes missing, and it
takes one second for the controller driver to time out and read the
response in the polling mode.

Although we aren't sure about the real culprit yet, in this patch, we
put a workaround by forcing the polling mode as default for CFL
machines; the polling mode itself isn't too heavy, and much better
than other workarounds initially suggested (e.g. disabling
power-save), at least.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199007
Fixes: e79b0006c45c ("ALSA: hda - Add Coffelake PCI ID")
Reported-and-tested-by: Hui Wang <hui.wang at canonical.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/pci/hda/hda_intel.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index d5017adf9feb..c507c69029e3 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -375,6 +375,7 @@ enum {
 					((pci)->device == 0x160c))
 
 #define IS_BXT(pci) ((pci)->vendor == 0x8086 && (pci)->device == 0x5a98)
+#define IS_CFL(pci) ((pci)->vendor == 0x8086 && (pci)->device == 0xa348)
 
 static char *driver_short_names[] = {
 	[AZX_DRIVER_ICH] = "HDA Intel",
@@ -1744,6 +1745,10 @@ static int azx_create(struct snd_card *card, struct pci_dev *pci,
 	else
 		chip->bdl_pos_adj = bdl_pos_adj[dev];
 
+	/* Workaround for a communication error on CFL (bko#199007) */
+	if (IS_CFL(pci))
+		chip->polling_mode = 1;
+
 	err = azx_bus_init(chip, model[dev], &pci_hda_io_ops);
 	if (err < 0) {
 		kfree(hda);
-- 
2.16.2