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 at wunner.de> --- drivers/gpu/drm/radeon/radeon_drv.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/gpu/drm/radeon/radeon_drv.c b/drivers/gpu/drm/radeon/radeon_drv.c index e266ffc..cad2555 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) -- 1.8.5.2 (Apple Git-48)
