diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
index af0d372..7aaaa57 100644
--- a/drivers/gpu/vga/vga_switcheroo.c
+++ b/drivers/gpu/vga/vga_switcheroo.c
@@ -73,9 +73,19 @@
  * there can thus be up to three clients: Two vga clients (GPUs) and one audio
  * client (on the discrete GPU). The code is mostly prepared to support
  * machines with more than two GPUs should they become available.
+ *
  * The GPU to which the outputs are currently switched is called the
  * active client in vga_switcheroo parlance. The GPU not in use is the
- * inactive client.
+ * inactive client. When the inactive client's DRM driver is loaded,
+ * it will be unable to probe the panel's EDID and hence depends on
+ * VBIOS to provide its display modes. If the VBIOS modes are bogus or
+ * if there is no VBIOS at all (which is common on the MacBook Pro),
+ * a client may alternatively request that the DDC lines are temporarily
+ * switched to it, provided that the handler supports this. Switching
+ * only the DDC lines and not the entire output avoids unnecessary
+ * flickering. On machines which are able to mux external connectors,
+ * VBIOS cannot know of attached displays so switching the DDC lines
+ * is the only option to retrieve the displays' EDID.
  */
 
 /**
@@ -125,6 +135,7 @@ static DEFINE_MUTEX(vgasr_mutex);
  * 	(counting only vga clients, not audio clients)
  * @clients: list of registered clients
  * @handler: registered handler
+ * @ddc_lock: protects access to DDC lines while they are temporarily switched
  *
  * vga_switcheroo private data. Currently only one vga_switcheroo instance
  * per system is supported.
@@ -141,6 +152,7 @@ struct vgasr_priv {
 	struct list_head clients;
 
 	struct vga_switcheroo_handler *handler;
+	struct mutex ddc_lock;
 };
 
 #define ID_BIT_AUDIO		0x100
@@ -155,6 +167,7 @@ static void vga_switcheroo_debugfs_fini(struct vgasr_priv *priv);
 /* only one switcheroo per system */
 static struct vgasr_priv vgasr_priv = {
 	.clients = LIST_HEAD_INIT(vgasr_priv.clients),
+	.ddc_lock = __MUTEX_INITIALIZER(vgasr_priv.ddc_lock),
 };
 
 static bool vga_switcheroo_ready(void)
@@ -221,12 +234,14 @@ EXPORT_SYMBOL(vga_switcheroo_register_handler);
 void vga_switcheroo_unregister_handler(void)
 {
 	mutex_lock(&vgasr_mutex);
+	mutex_lock(&vgasr_priv.ddc_lock);
 	vgasr_priv.handler = NULL;
 	if (vgasr_priv.active) {
 		pr_info("disabled\n");
 		vga_switcheroo_debugfs_fini(&vgasr_priv);
 		vgasr_priv.active = false;
 	}
+	mutex_unlock(&vgasr_priv.ddc_lock);
 	mutex_unlock(&vgasr_mutex);
 }
 EXPORT_SYMBOL(vga_switcheroo_unregister_handler);
@@ -414,6 +429,55 @@ void vga_switcheroo_client_fb_set(struct pci_dev *pdev,
 EXPORT_SYMBOL(vga_switcheroo_client_fb_set);
 
 /**
+ * vga_switcheroo_lock_ddc() - temporarily switch DDC lines to a given client
+ * @pdev: client pci device
+ *
+ * Temporarily switch DDC lines to the client identified by @pdev
+ * (but leave the outputs otherwise switched to where they are).
+ * This allows the inactive client to probe EDID. The DDC lines must
+ * afterwards be released by calling vga_switcheroo_unlock_ddc(),
+ * even if this function returns an error.
+ *
+ * Return: 0 on success or a negative int on error.
+ * Specifically, -ENODEV if no handler has registered or if the handler
+ * does not support switching the DDC lines. Also, a negative value
+ * returned by the handler is propagated back to the caller.
+ * The return value has merely an informational purpose for any caller
+ * which might be interested in it. It is acceptable to ignore the return
+ * value and simply rely on the result of the subsequent EDID probe,
+ * which will be NULL if DDC switching failed.
+ */
+int vga_switcheroo_lock_ddc(struct pci_dev *pdev)
+{
+	enum vga_switcheroo_client_id id;
+
+	mutex_lock(&vgasr_priv.ddc_lock);
+	if (!vgasr_priv.handler || !vgasr_priv.handler->switch_ddc)
+		return -ENODEV;
+
+	id = vgasr_priv.handler->get_client_id(pdev);
+	return vgasr_priv.handler->switch_ddc(id);
+}
+EXPORT_SYMBOL(vga_switcheroo_lock_ddc);
+
+/**
+ * vga_switcheroo_unlock_ddc() - release DDC lines after a temporary switch
+ *
+ * Release DDC lines after having temporarily switched them to a client.
+ * This must be called even if vga_switcheroo_lock_ddc() returned an error.
+ * Invoking this function without calling vga_switcheroo_lock_ddc() first
+ * is not allowed.
+ */
+void vga_switcheroo_unlock_ddc(void)
+{
+	if (WARN_ON_ONCE(!mutex_is_locked(&vgasr_priv.ddc_lock)))
+		return;
+
+	mutex_unlock(&vgasr_priv.ddc_lock);
+}
+EXPORT_SYMBOL(vga_switcheroo_unlock_ddc);
+
+/**
  * DOC: Manual switching and manual power control
  *
  * In this mode of use, the file /sys/kernel/debug/vgaswitcheroo/switch
diff --git a/include/linux/vga_switcheroo.h b/include/linux/vga_switcheroo.h
index c557511..f5899b6 100644
--- a/include/linux/vga_switcheroo.h
+++ b/include/linux/vga_switcheroo.h
@@ -84,9 +84,12 @@ enum vga_switcheroo_client_id {
  * 	vga clients. Currently only the radeon and amdgpu drivers use this.
  * 	The return value is ignored
  * @switchto: switch outputs to given client.
- * 	Mandatory. For muxless machines this should be a no-op. Returning 0
- * 	denotes success, anything else failure (in which case the switch is
- * 	aborted)
+ * 	Mandatory. For muxless machines this should be a no-op. If the mux
+ * 	is able to switch DDC separately, this should switch all pins except
+ * 	for the DDC lines. Returning 0 denotes success, anything else failure
+ * 	(in which case the switch is aborted)
+ * @switch_ddc: switch DDC lines to given client.
+ * 	Optional. Should return 0 on success or a negative int on failure
  * @power_state: cut or reinstate power of given client.
  * 	Optional. The return value is ignored
  * @get_client_id: determine if given pci device is integrated or discrete GPU.
@@ -98,6 +101,7 @@ enum vga_switcheroo_client_id {
 struct vga_switcheroo_handler {
 	int (*init)(void);
 	int (*switchto)(enum vga_switcheroo_client_id id);
+	int (*switch_ddc)(enum vga_switcheroo_client_id id);
 	int (*power_state)(enum vga_switcheroo_client_id id,
 			   enum vga_switcheroo_state state);
 	enum vga_switcheroo_client_id (*get_client_id)(struct pci_dev *pdev);
@@ -140,6 +144,9 @@ void vga_switcheroo_client_fb_set(struct pci_dev *dev,
 int vga_switcheroo_register_handler(struct vga_switcheroo_handler *handler);
 void vga_switcheroo_unregister_handler(void);
 
+int vga_switcheroo_lock_ddc(struct pci_dev *pdev);
+void vga_switcheroo_unlock_ddc(void);
+
 int vga_switcheroo_process_delayed_switch(void);
 
 enum vga_switcheroo_state vga_switcheroo_get_client_state(struct pci_dev *dev);
@@ -160,6 +167,8 @@ static inline int vga_switcheroo_register_audio_client(struct pci_dev *pdev,
 	const struct vga_switcheroo_client_ops *ops,
 	enum vga_switcheroo_client_id id) { return 0; }
 static inline void vga_switcheroo_unregister_handler(void) {}
+static inline int vga_switcheroo_lock_ddc(struct pci_dev *pdev) { return 0; }
+static inline void vga_switcheroo_unlock_ddc(void) {}
 static inline int vga_switcheroo_process_delayed_switch(void) { return 0; }
 static inline enum vga_switcheroo_state vga_switcheroo_get_client_state(struct pci_dev *dev) { return VGA_SWITCHEROO_ON; }
 
