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 | 36 ++++++++++++++++++++++++++++++------
1 file changed, 30 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index f5926bf..e11e585 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -93,6 +93,12 @@ struct detailed_mode_closure {
int modes;
};
+struct edid_support_rb_closure {
+ struct edid *edid;
+ bool valid_support_rb;
+ bool support_rb;
+};
+
#define LEVEL_DMT 0
#define LEVEL_GTF 1
#define LEVEL_GTF2 2
@@ -2017,23 +2023,41 @@ 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;
+ struct edid_support_rb_closure *closure = data;
+ struct edid *edid = closure->edid;
+
+ if (is_display_descriptor(r, EDID_DETAIL_MONITOR_RANGE)) {
+ if (edid->features & BIT(0) && r[10] == BIT(2)) {
+ closure->valid_support_rb = true;
+ closure->support_rb = (r[15] & 0x10) ? true : false;
+ }
+ }
}
/* 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,
+ .valid_support_rb = false,
+ .support_rb = false,
+ };
+
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.valid_support_rb)
+ return closure.support_rb;
}
return ((edid->input & DRM_EDID_INPUT_DIGITAL) != 0);
--
1.9.1
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