[PATCH v3 3/3] ALSA: hda: Disabled unused audio controller for Dell platforms with Switchable Graphics

[Kai-Heng Feng <kai.heng.feng@canonical.com>]

Some Dell platforms (Preicsion 7510/7710/7520/7720) have a BIOS option
"Switchable Graphics" (SG).

When SG is enabled, we have:
00:02.0 VGA compatible controller: Intel Corporation Device 591b (rev 04)
00:1f.3 Audio device: Intel Corporation CM238 HD Audio Controller (rev 31)
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc.  [AMD/ATI] Ellesmere [Polaris10]
01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere [Radeon RX 580]

The Intel Audio outputs all the sound, including HDMI audio. The audio
controller comes with AMD graphics doesn't get used.

When SG is disabled, we have:
00:1f.3 Audio device: Intel Corporation CM238 HD Audio Controller (rev 31)
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc.  [AMD/ATI] Ellesmere [Polaris10]
01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere [Radeon RX 580]

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 controller still exposes its
sysfs, so userspace still opens the control file and stream. If
userspace tries to output sound through the stream, it hangs when
runtime suspend kicks in:
[ 12.796265] snd_hda_intel 0000:01:00.1: Disabling via vga_switcheroo
[ 12.796367] snd_hda_intel 0000:01:00.1: Cannot lock devices!

Since the discrete audio controller isn't useful when SG enabled, we
should just disable the device.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
---
v3: Simplify dell_switchable_gfx_is_enabled() by returning bool instead
    of error code.
    Use DMI_DEV_TYPE_OEM_STRING to match Dell System.

v2: Mario suggested to squash the HDA part into the same series.

 sound/pci/hda/hda_intel.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index 7720e3102bcc..d9310616d5ca 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -49,6 +49,8 @@
 #include <linux/clocksource.h>
 #include <linux/time.h>
 #include <linux/completion.h>
+#include <linux/dell-common.h>
+#include <linux/dmi.h>
 
 #ifdef CONFIG_X86
 /* for snoop control */
@@ -1629,6 +1631,38 @@ static void check_msi(struct azx *chip)
 	}
 }
 
+#if IS_ENABLED(CONFIG_DELL_LAPTOP)
+static bool check_dell_switchable_gfx(struct pci_dev *pdev)
+{
+	bool (*dell_switchable_gfx_is_enabled_func)(void);
+	bool enabled;
+
+	/* Only need to check for Dell laptops and AIOs */
+	if (!dmi_find_device(DMI_DEV_TYPE_OEM_STRING, "Dell System", NULL) ||
+	    !(dmi_match(DMI_CHASSIS_TYPE, "10") ||
+	      dmi_match(DMI_CHASSIS_TYPE, "13")) ||
+	    !(pdev->vendor == PCI_VENDOR_ID_ATI ||
+	      pdev->vendor == PCI_VENDOR_ID_NVIDIA))
+		return false;
+
+	dell_switchable_gfx_is_enabled_func =
+		symbol_request(dell_switchable_gfx_is_enabled);
+	if (!dell_switchable_gfx_is_enabled_func)
+		return false;
+
+	enabled = dell_switchable_gfx_is_enabled_func();
+
+	symbol_put(dell_switchable_gfx_is_enabled);
+
+	return enabled;
+}
+#else
+static bool check_dell_switchable_gfx(struct pci_dev *pdev)
+{
+	return false;
+}
+#endif
+
 /* check the snoop mode availability */
 static void azx_check_snoop_available(struct azx *chip)
 {
@@ -1711,6 +1745,11 @@ static int azx_create(struct snd_card *card, struct pci_dev *pci,
 	if (err < 0)
 		return err;
 
+	if (check_dell_switchable_gfx(pci)) {
+		pci_disable_device(pci);
+		return -ENODEV;
+	}
+
 	hda = kzalloc(sizeof(*hda), GFP_KERNEL);
 	if (!hda) {
 		pci_disable_device(pci);
-- 
2.17.0