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 <[email protected]>
---
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
--
1.9.1
Hi allen,
I love your patch! Perhaps something to improve:
[auto build test WARNING on linus/master]
[also build test WARNING on v5.4-rc5 next-20191031]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
url: https://github.com/0day-ci/linux/commits/allen/drm-edid-fixup-EDID-1-3-and-1-4-judge-reduced-blanking-timings-logic/20191102-200357
base: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 1204c70d9dcba31164f78ad5d8c88c42335d51f8
If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <[email protected]>
smatch warnings:
drivers/gpu/drm/drm_edid.c:2042 drm_monitor_supports_rb() warn: always true condition '(closure.support_rb >= 0) => (0-255 >= 0)'
vim +2042 drivers/gpu/drm/drm_edid.c
2030
2031 /* EDID 1.4 defines this explicitly. For EDID 1.3, we guess, badly. */
2032 static bool
2033 drm_monitor_supports_rb(struct edid *edid)
2034 {
2035 struct edid_support_rb_closure closure = {
2036 .edid = edid,
2037 .support_rb = -1,
2038 };
2039
2040 if (edid->revision >= 4) {
2041 drm_for_each_detailed_block((u8 *)edid, is_rb, &closure);
> 2042 if (closure.support_rb >= 0)
2043 return closure.support_rb;
2044 }
2045
2046 return true;
2047 }
2048
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation