platform/x86: asus-wmi: Support the hardware GPU MUX on some laptops

Support the hardware GPU MUX switch available on some models. This
switch can toggle the MUX between:

- 0, Dedicated mode
- 1, Optimus mode

Optimus mode is the regular iGPU + dGPU available, while dedicated
mode switches the system to have only the dGPU available.
Signed-off-by: Luke D. Jones <luke@ljones.dev>
Link: https://lore.kernel.org/r/20220813092624.6228-1-luke@ljones.devReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Documentation/ABI/testing/sysfs-platform-asus-wmi

@@ -58,6 +58,18 @@ Description:
 			* 1 - overboost,
 			* 2 - silent
 
+What:		/sys/devices/platform/<platform>/gpu_mux_mode
+Date:		Aug 2022
+KernelVersion:	6.1
+Contact:	"Luke Jones" <luke@ljones.dev>
+Description:
+		Switch the GPU hardware MUX mode. Laptops with this feature can
+		can be toggled to boot with only the dGPU (discrete mode) or in
+		standard Optimus/Hybrid mode. On switch a reboot is required:
+
+			* 0 - Discrete GPU,
+			* 1 - Optimus/Hybrid,
+
 What:		/sys/devices/platform/<platform>/dgpu_disable
 Date:		Aug 2022
 KernelVersion:	5.17

drivers/platform/x86/asus-wmi.c

@@ -231,6 +231,7 @@ struct asus_wmi {
 
 	bool egpu_enable_available;
 	bool dgpu_disable_available;
+	bool gpu_mux_mode_available;
 
 	bool throttle_thermal_policy_available;
 	u8 throttle_thermal_policy_mode;
@@ -657,6 +658,52 @@ static ssize_t egpu_enable_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(egpu_enable);
 
+/* gpu mux switch *************************************************************/
+static ssize_t gpu_mux_mode_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct asus_wmi *asus = dev_get_drvdata(dev);
+	int result;
+
+	result = asus_wmi_get_devstate_simple(asus, ASUS_WMI_DEVID_GPU_MUX);
+	if (result < 0)
+		return result;
+
+	return sysfs_emit(buf, "%d\n", result);
+}
+
+static ssize_t gpu_mux_mode_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t count)
+{
+	struct asus_wmi *asus = dev_get_drvdata(dev);
+	int result, err;
+	u32 optimus;
+
+	err = kstrtou32(buf, 10, &optimus);
+	if (err)
+		return err;
+
+	if (optimus > 1)
+		return -EINVAL;
+
+	err = asus_wmi_set_devstate(ASUS_WMI_DEVID_GPU_MUX, optimus, &result);
+	if (err) {
+		dev_err(dev, "Failed to set GPU MUX mode: %d\n", err);
+		return err;
+	}
+	/* !1 is considered a fail by ASUS */
+	if (result != 1) {
+		dev_warn(dev, "Failed to set GPU MUX mode (result): 0x%x\n", result);
+		return -EIO;
+	}
+
+	sysfs_notify(&asus->platform_device->dev.kobj, NULL, "gpu_mux_mode");
+
+	return count;
+}
+static DEVICE_ATTR_RW(gpu_mux_mode);
+
 /* Battery ********************************************************************/
 
 /* The battery maximum charging percentage */
@@ -3172,6 +3219,7 @@ static struct attribute *platform_attributes[] = {
 	&dev_attr_touchpad.attr,
 	&dev_attr_egpu_enable.attr,
 	&dev_attr_dgpu_disable.attr,
+	&dev_attr_gpu_mux_mode.attr,
 	&dev_attr_lid_resume.attr,
 	&dev_attr_als_enable.attr,
 	&dev_attr_fan_boost_mode.attr,
@@ -3202,6 +3250,8 @@ static umode_t asus_sysfs_is_visible(struct kobject *kobj,
 		ok = asus->egpu_enable_available;
 	else if (attr == &dev_attr_dgpu_disable.attr)
 		ok = asus->dgpu_disable_available;
+	else if (attr == &dev_attr_gpu_mux_mode.attr)
+		ok = asus->gpu_mux_mode_available;
 	else if (attr == &dev_attr_fan_boost_mode.attr)
 		ok = asus->fan_boost_mode_available;
 	else if (attr == &dev_attr_throttle_thermal_policy.attr)
@@ -3465,6 +3515,7 @@ static int asus_wmi_add(struct platform_device *pdev)
 
 	asus->egpu_enable_available = asus_wmi_dev_is_present(asus, ASUS_WMI_DEVID_EGPU);
 	asus->dgpu_disable_available = asus_wmi_dev_is_present(asus, ASUS_WMI_DEVID_DGPU);
+	asus->gpu_mux_mode_available = asus_wmi_dev_is_present(asus, ASUS_WMI_DEVID_GPU_MUX);
 	asus->panel_overdrive_available = asus_wmi_dev_is_present(asus, ASUS_WMI_DEVID_PANEL_OD);
 
 	err = fan_boost_mode_check_present(asus);

include/linux/platform_data/x86/asus-wmi.h

@@ -99,6 +99,9 @@
 /* dgpu on/off */
 #define ASUS_WMI_DEVID_DGPU		0x00090020
 
+/* gpu mux switch, 0 = dGPU, 1 = Optimus */
+#define ASUS_WMI_DEVID_GPU_MUX		0x00090016
+
 /* DSTS masks */
 #define ASUS_WMI_DSTS_STATUS_BIT	0x00000001
 #define ASUS_WMI_DSTS_UNKNOWN_BIT	0x00000002