On Mon, Nov 04, 2019 at 04:42:49PM +0800, allen wrote:
> 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
That should probably be some new function:
bool is_display_descriptor(const u8 *desc, u8 tag);
is_display_descriptor(EDID_DETAIL_MONITOR_RANGE)
or something along those lines
We don't seem to check that in most places so should be rolled out all
over. The usage of struct detailed_timing all over also makes everything
rather confusing.
> Second: read detailed timing descriptor byte10 = 0x04 and
> EDID byte18h bit0 = 1
Indicates CVT support. Should give these things real names so
one wouldn't have to decode by hand.
> 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.c...@ite.com.tw>
> Reported-by: kbuild test robot <l...@intel.com>
> ---
> 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..9b67b80 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;
> + s8 support_rb;
bool
> +};
> +
> #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;
With the bool the ternary operator is not needed. Also should maybe
be |= in case we have multiple range descriptors? Not sure that is
legal.
> + }
> }
>
> /* 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;
Why are we now assuming rb for all pre 1.4 EDIDs?
> }
>
> static void
> --
> 1.9.1
>
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> dri-devel@lists.freedesktop.org
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--
Ville Syrjälä
Intel
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