drm/radeon: Defer probe if gmux is present but its driver isn't

gmux is a microcontroller built into dual GPU MacBook Pros.
On pre-retina MBPs, if we're the inactive GPU, we need apple-gmux
to temporarily switch DDC so that we can probe the panel's EDID.

The checks for CONFIG_VGA_ARB and CONFIG_VGA_SWITCHEROO are necessary
because if either of them is disabled but gmux is present, the driver
would never load, even if we're the active GPU. (vga_default_device()
would evaluate to NULL and vga_switcheroo_handler_flags() would
evaluate to 0.)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/552da6d85a82092146af7b0693595fa2a9ea376b.1452525860.git.lukas@wunner.de

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_drv.c b/drivers/gpu/drm/radeon/radeon_drv.c
index e266ffc520d2..cad25557650f 100644
--- a/drivers/gpu/drm/radeon/radeon_drv.c
+++ b/drivers/gpu/drm/radeon/radeon_drv.c
@@ -34,9 +34,11 @@
 #include "radeon_drv.h"
 
 #include <drm/drm_pciids.h>
+#include <linux/apple-gmux.h>
 #include <linux/console.h>
 #include <linux/module.h>
 #include <linux/pm_runtime.h>
+#include <linux/vgaarb.h>
 #include <linux/vga_switcheroo.h>
 #include <drm/drm_gem.h>
 
@@ -319,6 +321,15 @@ static int radeon_pci_probe(struct pci_dev *pdev,
 {
         int ret;
 
+        /*
+         * apple-gmux is needed on dual GPU MacBook Pro
+         * to probe the panel if we're the inactive GPU.
+         */
+        if (IS_ENABLED(CONFIG_VGA_ARB) && IS_ENABLED(CONFIG_VGA_SWITCHEROO) &&
+            apple_gmux_present() && pdev != vga_default_device() &&
+            !vga_switcheroo_handler_flags())
+                return -EPROBE_DEFER;
+
         /* Get rid of things like offb */
         ret = radeon_kick_out_firmware_fb(pdev);
         if (ret)