From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
The DSB has problems loading the legacy LUT. Looks like
simply writing each LUT entry twice back-to-back is
sufficient workaround for this.
Curiously it doesn't even matter what data we provide for the
first write, the second write always seems to work 100%. So
this doesn't seem to be some kind of simple race where the data
gets latched before it's actually available on some bus (which
was my first hunch).
TODO: need to figure out what is the actual hw issue here
Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/display/intel_color.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/display/intel_color.c b/drivers/gpu/drm/i915/display/intel_color.c
index 4c3344ee473e..8de2dc4b7904 100644
--- a/drivers/gpu/drm/i915/display/intel_color.c
+++ b/drivers/gpu/drm/i915/display/intel_color.c
@@ -860,9 +860,18 @@ static void ilk_load_lut_8(const struct intel_crtc_state *crtc_state,
lut = blob->data;
- for (i = 0; i < 256; i++)
+ for (i = 0; i < 256; i++) {
+ /*
+ * DSB fails to correctly load the legacy
+ * LUT unless we write each entry twice.
+ * It doesn't actually matter what data we
+ * provide for the first write.
+ */
+ if (crtc_state->dsb)
+ ilk_lut_write(crtc_state, LGC_PALETTE(pipe, i), 0);
ilk_lut_write(crtc_state, LGC_PALETTE(pipe, i),
i9xx_lut_8(&lut[i]));
+ }
}
static void ilk_load_lut_10(const struct intel_crtc_state *crtc_state,
--
2.38.2
