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[v2,18/22,EXPERIMENTAL] vga_switcheroo: Allow using active client as proxy when reading DDC/AUX

Message ID 9eed8ede6f15a254ad578e783b050e1c585d5a15.1439288957.git.lukas@wunner.de
State New, archived
Headers show

Commit Message

Lukas Wunner July 29, 2015, 7:23 p.m. UTC
The retina MacBook Pro uses an eDP panel and a gmux controller to switch
the panel between its two GPUs. Unfortunately it seems that it cannot
switch the AUX channel separately from the main link.

But we can emulate switching of DDC/AUX in software by using the active
client as a proxy to talk to the panel.

Allow storing pointers to each client's struct i2c_adapter (for DDC) and
struct drm_dp_aux. Allow retrieving the active client's structures but
constrain access to vga_switcheroo clients to prevent non-clients from
using proxying.

Drivers store AUX first, then DDC because they access the DPCD before
the EDID. Retrieving AUX is only allowed if DDC is also stored, thereby
avoiding race condition where AUX is already stored but not DDC and the
inactive client uses AUX then fails on retrieving the EDID via DDC.

Upon storing DDC, generate hotplug event so that already registered
inactive clients reprobe once the active client has registered its
DDC/AUX structures.

Based (loosely) on patches by Matthew Garrett <mjg59@srcf.ucam.org>
who let the active client stash the EDID and the first 8 bytes of the
DPCD (receiver capabilities) in vga_switcheroo where the inactive client
would subsequently pick it up. It turns out that the drivers are unhappy
with just 8 bytes of DPCD, they need access to the full DPCD to set up
their outputs. Switching in software gives us more options (even write
access to the DPCD if need be):

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Tested-by: Paul Hordiienko <pvt.gord@gmail.com>
    [MBP  6,2 2010  intel ILK + nvidia GT216  pre-retina]
Tested-by: William Brown <william@blackhats.net.au>
    [MBP  8,2 2011  intel SNB + amd turks     pre-retina]
Tested-by: Lukas Wunner <lukas@wunner.de>
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina]
Tested-by: Bruno Bierbaumer <bruno@bierbaumer.net>
    [MBP 11,3 2013  intel HSW + nvidia GK107  retina -- work in progress]

Signed-off-by: Lukas Wunner <lukas@wunner.de>
 drivers/gpu/vga/vga_switcheroo.c | 62 ++++++++++++++++++++++++++++++++++++++++
 include/linux/vga_switcheroo.h   | 11 +++++++
 2 files changed, 73 insertions(+)
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diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
index 94b0b6f..0c52eb4 100644
--- a/drivers/gpu/vga/vga_switcheroo.c
+++ b/drivers/gpu/vga/vga_switcheroo.c
@@ -19,6 +19,7 @@ 
 #include <drm/drm_crtc_helper.h>
+#include <drm/drm_dp_helper.h>
 #include <linux/module.h>
 #include <linux/seq_file.h>
@@ -27,6 +28,7 @@ 
 #include <linux/debugfs.h>
 #include <linux/fb.h>
+#include <linux/i2c.h>
 #include <linux/pci.h>
 #include <linux/console.h>
 #include <linux/vga_switcheroo.h>
@@ -37,6 +39,8 @@ 
 struct vga_switcheroo_client {
 	struct pci_dev *pdev;
 	struct fb_info *fb_info;
+	struct i2c_adapter *ddc;
+	struct drm_dp_aux *aux;
 	struct work_struct reprobe_work;
 	int pwr_state;
 	const struct vga_switcheroo_client_ops *ops;
@@ -355,6 +359,64 @@  out:
+void vga_switcheroo_set_ddc(struct pci_dev *pdev, struct i2c_adapter *ddc)
+	struct vga_switcheroo_client *client;
+	mutex_lock(&vgasr_mutex);
+	client = find_client_from_pci(&vgasr_priv.clients, pdev);
+	if (client)
+		client->ddc = ddc;
+	mutex_unlock(&vgasr_mutex);
+	/* DDC is stored after AUX on eDP, so we have both now */
+	if (client->active)
+		vga_switcheroo_reprobe_inactive_clients();
+struct i2c_adapter *vga_switcheroo_get_ddc(struct pci_dev *pdev)
+	struct vga_switcheroo_client *active = NULL;
+	mutex_lock(&vgasr_mutex);
+	if (find_client_from_pci(&vgasr_priv.clients, pdev))
+		active = find_active_client(&vgasr_priv.clients);
+	mutex_unlock(&vgasr_mutex);
+	if (!active)
+		return NULL;
+	return active->ddc;
+void vga_switcheroo_set_aux(struct pci_dev *pdev, struct drm_dp_aux *aux)
+	struct vga_switcheroo_client *client;
+	mutex_lock(&vgasr_mutex);
+	client = find_client_from_pci(&vgasr_priv.clients, pdev);
+	if (client)
+		client->aux = aux;
+	mutex_unlock(&vgasr_mutex);
+struct drm_dp_aux *vga_switcheroo_get_aux(struct pci_dev *pdev)
+	struct vga_switcheroo_client *active = NULL;
+	mutex_lock(&vgasr_mutex);
+	if (find_client_from_pci(&vgasr_priv.clients, pdev))
+		active = find_active_client(&vgasr_priv.clients);
+	mutex_unlock(&vgasr_mutex);
+	if (!active || !active->ddc)
+		return NULL;
+	return active->aux;
 static int vga_switcheroo_show(struct seq_file *m, void *v)
 	struct vga_switcheroo_client *client;
diff --git a/include/linux/vga_switcheroo.h b/include/linux/vga_switcheroo.h
index b935d83..1d4c07e 100644
--- a/include/linux/vga_switcheroo.h
+++ b/include/linux/vga_switcheroo.h
@@ -10,7 +10,10 @@ 
+#include <drm/drm_dp_helper.h>
 #include <linux/fb.h>
+#include <linux/i2c.h>
 struct pci_dev;
@@ -56,6 +59,10 @@  void vga_switcheroo_client_fb_set(struct pci_dev *dev,
 int vga_switcheroo_lock_ddc(struct pci_dev *pdev);
 int vga_switcheroo_unlock_ddc(struct pci_dev *pdev);
+void vga_switcheroo_set_ddc(struct pci_dev *pdev, struct i2c_adapter *ddc);
+struct i2c_adapter *vga_switcheroo_get_ddc(struct pci_dev *pdev);
+void vga_switcheroo_set_aux(struct pci_dev *pdev, struct drm_dp_aux *aux);
+struct drm_dp_aux *vga_switcheroo_get_aux(struct pci_dev *pdev);
 int vga_switcheroo_register_handler(struct vga_switcheroo_handler *handler);
 void vga_switcheroo_unregister_handler(void);
@@ -77,6 +84,10 @@  static inline int vga_switcheroo_register_client(struct pci_dev *dev,
 static inline void vga_switcheroo_client_fb_set(struct pci_dev *dev, struct fb_info *info) {}
 static inline int vga_switcheroo_lock_ddc(struct pci_dev *pdev) { return -ENODEV; }
 static inline int vga_switcheroo_unlock_ddc(struct pci_dev *pdev) { return -ENODEV; }
+static inline void vga_switcheroo_set_ddc(struct pci_dev *pdev, struct i2c_adapter *ddc) {}
+static inline struct i2c_adapter *vga_switcheroo_get_ddc(struct pci_dev *pdev) { return NULL; }
+static inline void vga_switcheroo_set_aux(struct pci_dev *pdev, struct drm_dp_aux *aux) {}
+static inline struct drm_dp_aux *vga_switcheroo_get_aux(struct pci_dev *pdev) { return NULL; }
 static inline int vga_switcheroo_register_handler(struct vga_switcheroo_handler *handler) { return 0; }
 static inline int vga_switcheroo_register_audio_client(struct pci_dev *pdev,
 	const struct vga_switcheroo_client_ops *ops,