Refer to EDID 1.3 spec, display FEATURE (byte 18h) bit #0 said "If this bit is set to 1, the display supports timings based on the GTF standard using default GTF parameter values".
And EDID 1.4 spec shows "If bit 0 is set to 0, then the display is noncontinuous frequency (multi-mode) and is only specified to accept the video timing formats that are listed in BASE EDID and certain EXTENSION Blocks.
When display feature did not support CVT or GFT2 and monitor's EDID version greater than or equal to "1.2". DRM driver would select GTF as default for standard timing calculation. It may generated some video timing that can't display properly by external monitor.
For example. When driver retrieved "0xD1 0xFC" (FHD, 120Hz) and "0xD1 0xE8" (FHD, 100Hz) from "Standard Timings". GTF formula would generate video timing like below. It already over monitor's spec to cause black screen issue. "1920x1080" 120 368881 1920 2072 2288 2656 1080 1081 1084 1157 0x0 0x6 "1920x1080" 100 301992 1920 2072 2280 2640 1080 1081 1084 1144 0x0 0x6
v2: Just confirm GTF flag and omit the revision check.
Cc: Jani Nikula jani.nikula@intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: Adam Jackson ajax@redhat.com Cc: Cooper Chiou cooper.chiou@intel.com Signed-off-by: Lee Shawn C shawn.c.lee@intel.com --- drivers/gpu/drm/drm_edid.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index 5aee0ebc200e..26eb04820b52 100644 --- a/drivers/gpu/drm/drm_edid.c +++ b/drivers/gpu/drm/drm_edid.c @@ -2193,7 +2193,8 @@ static int standard_timing_level(struct edid *edid) return LEVEL_CVT; if (drm_gtf2_hbreak(edid)) return LEVEL_GTF2; - return LEVEL_GTF; + if (edid->features & DRM_EDID_FEATURE_DEFAULT_GTF) + return LEVEL_GTF; } return LEVEL_DMT; }