Hi Jani Thanks for your help and I will follow your suggestion to modify the patch. -----Original Message----- From: Jani Nikula [mailto:jani.nikula@xxxxxxxxxxxxxxx] Sent: Tuesday, December 10, 2019 7:10 PM To: Allen Chen (陳柏宇) Cc: Jau-Chih Tseng (曾昭智); Maxime Ripard; Allen Chen (陳柏宇); open list; open list:DRM DRIVERS; David Airlie; Pi-Hsun Shih; Sean Paul Subject: Re: [PATCH] drm/edid: fixup EDID 1.3 and 1.4 judge reduced-blanking timings logic On Tue, 26 Nov 2019, allen <allen.chen@xxxxxxxxxx> 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 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.chen@xxxxxxxxxx> > Reported-by: kbuild test robot <lkp@xxxxxxxxx> > --- > 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)) { I'll try to explain my original comment again. Consider edid->features & BIT(0). It remains unchanged across the iteration. The code will only change anything if edid->features & BIT(0). > + closure->valid_support_rb = true; > + closure->support_rb = (r[15] & 0x10) ? true : false; You could combine these to e.g. a single int. if (r[10] == BIT(2)) { int *ret = data; *ret = !!(r[15] & 0x10); } > + } > + } > } > > /* 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; Here, you'd do: 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); -- Jani Nikula, Intel Open Source Graphics Center _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
