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://bugzilla.kernel.org/show_bug.cgi?id=88861 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115 Tested-by: Lukas Wunner lukas@wunner.de [MBP 9,1 2012 intel IVB + nvidia GK107 pre-retina 15"] Signed-off-by: Lukas Wunner lukas@wunner.de --- drivers/gpu/drm/nouveau/nouveau_drm.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c index 2f2f252..bb8498c 100644 --- a/drivers/gpu/drm/nouveau/nouveau_drm.c +++ b/drivers/gpu/drm/nouveau/nouveau_drm.c @@ -22,11 +22,13 @@ * Authors: Ben Skeggs */
+#include <linux/apple-gmux.h> #include <linux/console.h> #include <linux/delay.h> #include <linux/module.h> #include <linux/pci.h> #include <linux/pm_runtime.h> +#include <linux/vgaarb.h> #include <linux/vga_switcheroo.h>
#include "drmP.h" @@ -312,6 +314,15 @@ static int nouveau_drm_probe(struct pci_dev *pdev, bool boot = false; 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; + /* remove conflicting drivers (vesafb, efifb etc) */ aper = alloc_apertures(3); if (!aper)