[alsa-devel] [PATCH v4 3/3] ALSA: hda: Disabled unused audio controller for Dell platforms with Switchable Graphics

[Kai-Heng Feng]

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 contoller still exposes its
sysfs, so userspace still opens the control file and stream. If
userspace tries to output sound through the stream, it hangs the system.

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

Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
---
v4: Change the commit message to clarify there's no more runtime pm
    warning.
    Also skip the check for thunderbolt attached devices.

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 | 43 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index 7a111a1b5836..3981193c8d29 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 */
@@ -1627,6 +1629,42 @@ 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;
+
+	/* Thunderbolt devices won't be switchable */
+	if (pci_is_thunderbolt_attached(pdev))
+		return false;
+
+	/* Only 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)
 {
@@ -1709,6 +1747,11 @@ 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