platform/x86: asus-wmi: add safety checks to gpu switching

Add safety checking to dgpu_disable, egpu_enable, gpu_mux_mode.

These checks prevent users from doing such things as:
- disabling the dGPU while is muxed to drive the internal screen
- enabling the eGPU which also disables the dGPU, while muxed to
  the internal screen
- switching the MUX to dGPU while the dGPU is disabled

Signed-off-by: Luke D. Jones <luke@ljones.dev>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230630053552.976579-7-luke@ljones.dev
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/asus-wmi.c

@@ -645,6 +645,18 @@ static ssize_t dgpu_disable_store(struct device *dev,
 	if (disable > 1)
 		return -EINVAL;
 
+	if (asus->gpu_mux_mode_available) {
+		result = asus_wmi_get_devstate_simple(asus, ASUS_WMI_DEVID_GPU_MUX);
+		if (result < 0)
+			/* An error here may signal greater failure of GPU handling */
+			return result;
+		if (!result && disable) {
+			err = -ENODEV;
+			pr_warn("Can not disable dGPU when the MUX is in dGPU mode: %d\n", err);
+			return err;
+		}
+	}
+
 	err = asus_wmi_set_devstate(ASUS_WMI_DEVID_DGPU, disable, &result);
 	if (err) {
 		pr_warn("Failed to set dgpu disable: %d\n", err);
@@ -702,6 +714,18 @@ static ssize_t egpu_enable_store(struct device *dev,
 		return err;
 	}
 
+	if (asus->gpu_mux_mode_available) {
+		result = asus_wmi_get_devstate_simple(asus, ASUS_WMI_DEVID_GPU_MUX);
+		if (result < 0)
+			/* An error here may signal greater failure of GPU handling */
+			return result;
+		if (!result && enable) {
+			err = -ENODEV;
+			pr_warn("Can not enable eGPU when the MUX is in dGPU mode: %d\n", err);
+			return err;
+		}
+	}
+
 	err = asus_wmi_set_devstate(ASUS_WMI_DEVID_EGPU, enable, &result);
 	if (err) {
 		pr_warn("Failed to set egpu disable: %d\n", err);
@@ -764,6 +788,30 @@ static ssize_t gpu_mux_mode_store(struct device *dev,
 	if (optimus > 1)
 		return -EINVAL;
 
+	if (asus->dgpu_disable_available) {
+		result = asus_wmi_get_devstate_simple(asus, ASUS_WMI_DEVID_DGPU);
+		if (result < 0)
+			/* An error here may signal greater failure of GPU handling */
+			return result;
+		if (result && !optimus) {
+			err = -ENODEV;
+			pr_warn("Can not switch MUX to dGPU mode when dGPU is disabled: %d\n", err);
+			return err;
+		}
+	}
+
+	if (asus->egpu_enable_available) {
+		result = asus_wmi_get_devstate_simple(asus, ASUS_WMI_DEVID_EGPU);
+		if (result < 0)
+			/* An error here may signal greater failure of GPU handling */
+			return result;
+		if (result && !optimus) {
+			err = -ENODEV;
+			pr_warn("Can not switch MUX to dGPU mode when eGPU is enabled: %d\n", err);
+			return err;
+		}
+	}
+
 	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);