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 byte 0 = 0x00,
byte 1 = 0x00, byte 2 = 0x00 and byte 3 = 0xFD
Second: read EDID bit 0 in feature support byte at address 18h = 1
and detailed timing descriptor byte 10 = 0x04
Third: if EDID bit 0 in feature support byte = 1 &&
detailed timing descriptor byte 10 = 0x04
then we can check byte 15, if bit 4 in byte 15 = 1 is support RB
if EDID bit 0 in feature support byte != 1 ||
detailed timing descriptor byte 10 != 0x04,
then byte 15 can not be used
The linux code is_rb function not follow the VESA's rule
Signed-off-by: Allen Chen <allen.c...@ite.com.tw>
Reported-by: kbuild test robot <l...@intel.com>
---
drivers/gpu/drm/drm_edid.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index f5926bf..826ed78 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -2017,13 +2017,21 @@ struct drm_display_mode *drm_mode_find_dmt(struct
drm_device *dev,
}
}
+static bool
+is_display_descriptor(const u8 *r, u8 tag)
+{
+ return (!r[0] && !r[1] && !r[2] && r[3] == tag) ? true : false;
+}
+
static void
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;
+
+ if (is_display_descriptor(r, EDID_DETAIL_MONITOR_RANGE)) {
+ if (r[10] == BIT(2))
+ *(int *)data = !!(r[15] & 0x10);
+ }
}
/* EDID 1.4 defines this explicitly. For EDID 1.3, we guess, badly. */
@@ -2031,9 +2039,13 @@ struct drm_display_mode *drm_mode_find_dmt(struct
drm_device *dev,
drm_monitor_supports_rb(struct edid *edid)
{
if (edid->revision >= 4) {
- bool ret = false;
- drm_for_each_detailed_block((u8 *)edid, is_rb, &ret);
- return ret;
+ if (edid->features & BIT(0)) {
+ int ret = -1;
+
+ drm_for_each_detailed_block((u8 *)edid, is_rb, &ret);
+ if (ret != -1)
+ return ret;
+ }
}
return ((edid->input & DRM_EDID_INPUT_DIGITAL) != 0);
--
1.9.1
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