[2/3] platform/x86: apple-gmux: Add apple_gmux_detect() helper

diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
index a0af01f6a0fd..9333f82cfa8a 100644
--- a/drivers/platform/x86/apple-gmux.c
+++ b/drivers/platform/x86/apple-gmux.c
@@ -226,23 +226,6 @@  static void gmux_write32(struct apple_gmux_data *gmux_data, int port,
 		gmux_pio_write32(gmux_data, port, val);
 }
 
-static bool gmux_is_indexed(struct apple_gmux_data *gmux_data)
-{
-	u16 val;
-
-	outb(0xaa, gmux_data->iostart + 0xcc);
-	outb(0x55, gmux_data->iostart + 0xcd);
-	outb(0x00, gmux_data->iostart + 0xce);
-
-	val = inb(gmux_data->iostart + 0xcc) |
-		(inb(gmux_data->iostart + 0xcd) << 8);
-
-	if (val == 0x55aa)
-		return true;
-
-	return false;
-}
-
 /**
  * DOC: Backlight control
  *
@@ -582,60 +565,43 @@  static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
 	int ret = -ENXIO;
 	acpi_status status;
 	unsigned long long gpe;
+	bool indexed = false;
+	u32 version;
 
 	if (apple_gmux_data)
 		return -EBUSY;
 
+	if (!apple_gmux_detect(pnp, &indexed)) {
+		pr_info("gmux device not present\n");
+		return -ENODEV;
+	}
+
 	gmux_data = kzalloc(sizeof(*gmux_data), GFP_KERNEL);
 	if (!gmux_data)
 		return -ENOMEM;
 	pnp_set_drvdata(pnp, gmux_data);
 
 	res = pnp_get_resource(pnp, IORESOURCE_IO, 0);
-	if (!res) {
-		pr_err("Failed to find gmux I/O resource\n");
-		goto err_free;
-	}
-
 	gmux_data->iostart = res->start;
 	gmux_data->iolen = resource_size(res);
 
-	if (gmux_data->iolen < GMUX_MIN_IO_LEN) {
-		pr_err("gmux I/O region too small (%lu < %u)\n",
-		       gmux_data->iolen, GMUX_MIN_IO_LEN);
-		goto err_free;
-	}
-
 	if (!request_region(gmux_data->iostart, gmux_data->iolen,
 			    "Apple gmux")) {
 		pr_err("gmux I/O already in use\n");
 		goto err_free;
 	}
 
-	/*
-	 * Invalid version information may indicate either that the gmux
-	 * device isn't present or that it's a new one that uses indexed
-	 * io
-	 */
-
-	ver_major = gmux_read8(gmux_data, GMUX_PORT_VERSION_MAJOR);
-	ver_minor = gmux_read8(gmux_data, GMUX_PORT_VERSION_MINOR);
-	ver_release = gmux_read8(gmux_data, GMUX_PORT_VERSION_RELEASE);
-	if (ver_major == 0xff && ver_minor == 0xff && ver_release == 0xff) {
-		if (gmux_is_indexed(gmux_data)) {
-			u32 version;
-			mutex_init(&gmux_data->index_lock);
-			gmux_data->indexed = true;
-			version = gmux_read32(gmux_data,
-				GMUX_PORT_VERSION_MAJOR);
-			ver_major = (version >> 24) & 0xff;
-			ver_minor = (version >> 16) & 0xff;
-			ver_release = (version >> 8) & 0xff;
-		} else {
-			pr_info("gmux device not present\n");
-			ret = -ENODEV;
-			goto err_release;
-		}
+	if (indexed) {
+		mutex_init(&gmux_data->index_lock);
+		gmux_data->indexed = true;
+		version = gmux_read32(gmux_data, GMUX_PORT_VERSION_MAJOR);
+		ver_major = (version >> 24) & 0xff;
+		ver_minor = (version >> 16) & 0xff;
+		ver_release = (version >> 8) & 0xff;
+	} else {
+		ver_major = gmux_read8(gmux_data, GMUX_PORT_VERSION_MAJOR);
+		ver_minor = gmux_read8(gmux_data, GMUX_PORT_VERSION_MINOR);
+		ver_release = gmux_read8(gmux_data, GMUX_PORT_VERSION_RELEASE);
 	}
 	pr_info("Found gmux version %d.%d.%d [%s]\n", ver_major, ver_minor,
 		ver_release, (gmux_data->indexed ? "indexed" : "classic"));
diff --git a/include/linux/apple-gmux.h b/include/linux/apple-gmux.h
index 80efaaf89e07..47c04e7e3672 100644
--- a/include/linux/apple-gmux.h
+++ b/include/linux/apple-gmux.h
@@ -8,6 +8,8 @@ 
 #define LINUX_APPLE_GMUX_H
 
 #include <linux/acpi.h>
+#include <linux/io.h>
+#include <linux/pnp.h>
 
 #define GMUX_ACPI_HID "APP000B"
 
@@ -35,14 +37,88 @@ 
 #define GMUX_MIN_IO_LEN			(GMUX_PORT_BRIGHTNESS + 4)
 
 #if IS_ENABLED(CONFIG_APPLE_GMUX)
+static inline bool apple_gmux_is_indexed(unsigned long iostart)
+{
+	u16 val;
+
+	outb(0xaa, iostart + 0xcc);
+	outb(0x55, iostart + 0xcd);
+	outb(0x00, iostart + 0xce);
+
+	val = inb(iostart + 0xcc) | (inb(iostart + 0xcd) << 8);
+	if (val == 0x55aa)
+		return true;
+
+	return false;
+}
 
 /**
- * apple_gmux_present() - detect if gmux is built into the machine
+ * apple_gmux_detect() - detect if gmux is built into the machine
+ *
+ * @pnp_dev:     Device to probe or NULL to use the first matching device
+ * @indexed_ret: Returns (by reference) if the gmux is indexed or not
+ *
+ * Detect if a supported gmux device is present by actually probing it.
+ * This avoids the false positives returned on some models by
+ * apple_gmux_present().
+ *
+ * Return: %true if a supported gmux ACPI device is detected and the kernel
+ * was configured with CONFIG_APPLE_GMUX, %false otherwise.
+ */
+static inline bool apple_gmux_detect(struct pnp_dev *pnp_dev, bool *indexed_ret)
+{
+	u8 ver_major, ver_minor, ver_release;
+	struct resource *res;
+	bool indexed = false;
+
+	if (!pnp_dev) {
+		struct acpi_device *adev;
+		struct device *dev;
+
+		adev = acpi_dev_get_first_match_dev(GMUX_ACPI_HID, NULL, -1);
+		if (!adev)
+			return false;
+
+		dev = acpi_get_first_physical_node(adev);
+		if (!dev)
+			return false;
+
+		pnp_dev = to_pnp_dev(dev);
+	}
+
+	res = pnp_get_resource(pnp_dev, IORESOURCE_IO, 0);
+	if (!res)
+		return false;
+
+	if (resource_size(res) < GMUX_MIN_IO_LEN)
+		return false;
+
+	/*
+	 * Invalid version information may indicate either that the gmux
+	 * device isn't present or that it's a new one that uses indexed io.
+	 */
+	ver_major = inb(res->start + GMUX_PORT_VERSION_MAJOR);
+	ver_minor = inb(res->start + GMUX_PORT_VERSION_MINOR);
+	ver_release = inb(res->start + GMUX_PORT_VERSION_RELEASE);
+	if (ver_major == 0xff && ver_minor == 0xff && ver_release == 0xff) {
+		indexed = apple_gmux_is_indexed(res->start);
+		if (!indexed)
+			return false;
+	}
+
+	if (indexed_ret)
+		*indexed_ret = indexed;
+
+	return true;
+}
+
+/**
+ * apple_gmux_present() - check if gmux ACPI device is present
  *
  * Drivers may use this to activate quirks specific to dual GPU MacBook Pros
  * and Mac Pros, e.g. for deferred probing, runtime pm and backlight.
  *
- * Return: %true if gmux is present and the kernel was configured
+ * Return: %true if gmux ACPI device is present and the kernel was configured
  * with CONFIG_APPLE_GMUX, %false otherwise.
  */
 static inline bool apple_gmux_present(void)
@@ -57,6 +133,11 @@  static inline bool apple_gmux_present(void)
 	return false;
 }
 
+static inline bool apple_gmux_detect(struct pnp_dev *pnp_dev, bool *indexed_ret)
+{
+	return false;
+}
+
 #endif /* !CONFIG_APPLE_GMUX */
 
 #endif /* LINUX_APPLE_GMUX_H */