According to VESA ENHANCED EXTENDED DISPLAY IDENTIFICATION DATA STANDARD (Defines EDID Structure Version 1, Revision 4) page: 39 How to determine whether the monitor support RB timing or not? EDID 1.4 First: read detailed timing descriptor and make sure byte0 = 0, byte1 = 0, byte2 = 0 and byte3 = 0xFD Second: read detailed timing descriptor byte10 = 0x04 and EDID byte18h bit0 = 1 Third: if EDID byte18h bit0 == 1 && byte10 == 0x04, then we can check byte15, if byte15 bit4 =1 is support RB if EDID byte18h bit0 != 1 || byte10 != 0x04, then byte15 can not be used

The linux code is_rb function not follow the VESA's rule

EDID 1.3 LCD flat panels do not require long blanking intervals as a retrace period so default support reduced-blanking timings.

Signed-off-by: Allen Chen allen.chen@ite.com.tw --- drivers/gpu/drm/drm_edid.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index e5e7e65..08e914d 100644 --- a/drivers/gpu/drm/drm_edid.c +++ b/drivers/gpu/drm/drm_edid.c @@ -93,6 +93,11 @@ struct detailed_mode_closure { int modes; };

+struct edid_support_rb_closure { + struct edid *edid; + u8 support_rb; +}; + #define LEVEL_DMT 0 #define LEVEL_GTF 1 #define LEVEL_GTF2 2 @@ -2018,22 +2023,31 @@ struct drm_display_mode *drm_mode_find_dmt(struct drm_device *dev, is_rb(struct detailed_timing *t, void *data) { u8 *r = (u8 *)t; - if (r[3] == EDID_DETAIL_MONITOR_RANGE) - if (r[15] & 0x10) - *(bool *)data = true; + struct edid_support_rb_closure *closure = data; + struct edid *edid = closure->edid; + + if (!r[0] && !r[1] && !r[2] && r[3] == EDID_DETAIL_MONITOR_RANGE) { + if (edid->features & BIT(0) && r[10] == BIT(2)) + closure->support_rb = (r[15] & 0x10) ? 1 : 0; + } }

/* EDID 1.4 defines this explicitly. For EDID 1.3, we guess, badly. */ static bool drm_monitor_supports_rb(struct edid *edid) { + struct edid_support_rb_closure closure = { + .edid = edid, + .support_rb = -1, + }; + if (edid->revision >= 4) { - bool ret = false; - drm_for_each_detailed_block((u8 *)edid, is_rb, &ret); - return ret; + drm_for_each_detailed_block((u8 *)edid, is_rb, &closure); + if (closure.support_rb >= 0) + return closure.support_rb; }

- return ((edid->input & DRM_EDID_INPUT_DIGITAL) != 0); + return true; }

static void