Thanks for the quick fix! Comments below...
On 08/12/2015 11:43 AM, Daniel Vetter wrote:
In
commit d328c9d78d64ca11e744fe227096990430a88477
Author: Daniel Vetter <daniel.vetter@xxxxxxxx>
Date: Fri Apr 10 16:22:37 2015 +0200
drm/i915: Select starting pipe bpp irrespective or the primary plane
we started to select the pipe bpp from sink capabilities and not from
the primary framebuffer - that one might change (and we don't want to
incur a modeset) and sprites might contain higher bpp content too.
Problem is that now if you have a 10bpc screen and display 24bpp rgb
primary then we select dithering, and apparently that mangles the high
8 bits even (even thought you'd expect dithering only to affect how
12bpc gets mapped into 10bpc). And that mangling upsets certain users.
Probably doesn't matter, but your explanation of the former problem here
is slightly off. We also selected dithering on a 8 bpc screen displaying
a 24bpp rgb primary, because pipe_bpp is 24 for such a typical 8 bpc
sink, but since the commit mentioned above, base_bpp is always the
absolute maximum supported by the hardware, e.g., 36 bpp on my Ironlake
chip. Iow. the only way to not get dithering would have been to connect
a deep color 12 bpc display, so pipe_bpp == 36 == base_bpp.
Hence only enable dithering on 6bpc screens where we difinitely and
always want it.
Other than that, i tested the patch on both 8 bpc output with my
measurement equipment and on the internal laptop 6 bpc panel, and
everything is fine now - No banding on the 6 bpc panel, no banding or
equipment failure on the external 8 bpc output. Life is good again :)
Reviewed-and-tested-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
thanks,
-mario
Cc: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
Reported-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_display.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 9a2f229a1c3a..128462e0a0b5 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12186,7 +12186,9 @@ encoder_retry:
goto encoder_retry;
}
- pipe_config->dither = pipe_config->pipe_bpp != base_bpp;
+ /* Dithering seems to not pass-through bits correctly when it should, so
+ * only enable it on 6bpc panels. */
+ pipe_config->dither = pipe_config->pipe_bpp == 6*3;
DRM_DEBUG_KMS("plane bpp: %i, pipe bpp: %i, dithering: %i\n",
base_bpp, pipe_config->pipe_bpp, pipe_config->dither);
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