drm/edid: Make the detailed timing CEA/HDMI mode fixup accept up to 5kHz clock difference

Rather than using drm_match_cea_mode() to see if the EDID detailed
timings are supposed to represent one of the CEA/HDMI modes, add a
special version of that function that takes in an explicit clock
tolerance value (in kHz). When looking at the detailed timings specify
the tolerance as 5kHz due to the 10kHz clock resolution limit inherent
in detailed timings.

drm_match_cea_mode() uses the normal KHZ2PICOS() matching of clocks,
which only allows smaller errors for lower clocks (eg. for 25200 it
won't allow any error) and a bigger error for higher clocks (eg. for
297000 it actually matches 296913-297000). So it doesn't really match
what we want for the fixup. Using the explicit +-5kHz is much better
for this use case.

Not sure if we should change the normal mode matching to also use
something else besides KHZ2PICOS() since it allows a different
proportion of error depending on the clock. I believe VESA CVT
allows a maximum deviation of .5%, so using that for normal mode
matching might be a good idea?

Cc: Adam Jackson <ajax@redhat.com>
Tested-by: nathan.d.ciobanu@linux.intel.com
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92217
Fixes: fa3a7340eaa1 ("drm/edid: Fix up clock for CEA/HDMI modes specified via detailed timings")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 18 insertions, 1 deletions

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index bde9b2911dc2..ef6bd3656548 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -917,13 +917,30 @@ bool drm_mode_equal(const struct drm_display_mode *mode1, const struct drm_displ
 	} else if (mode1->clock != mode2->clock)
 		return false;
 
+	return drm_mode_equal_no_clocks(mode1, mode2);
+}
+EXPORT_SYMBOL(drm_mode_equal);
+
+/**
+ * drm_mode_equal_no_clocks - test modes for equality
+ * @mode1: first mode
+ * @mode2: second mode
+ *
+ * Check to see if @mode1 and @mode2 are equivalent, but
+ * don't check the pixel clocks.
+ *
+ * Returns:
+ * True if the modes are equal, false otherwise.
+ */
+bool drm_mode_equal_no_clocks(const struct drm_display_mode *mode1, const struct drm_display_mode *mode2)
+{
 	if ((mode1->flags & DRM_MODE_FLAG_3D_MASK) !=
 	    (mode2->flags & DRM_MODE_FLAG_3D_MASK))
 		return false;
 
 	return drm_mode_equal_no_clocks_no_stereo(mode1, mode2);
 }
-EXPORT_SYMBOL(drm_mode_equal);
+EXPORT_SYMBOL(drm_mode_equal_no_clocks);
 
 /**
  * drm_mode_equal_no_clocks_no_stereo - test modes for equality