[PATCH v2 4/4] drm/i915: W/A for underruns with WM1+ disabled on icl

Ville Syrjala
2019-02-04T20:22:35Z

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

Disabling WM1+ on ICL causes tons of underruns with
linear/X-tiled framebuffers. We can avoid this by flipping
on a chicken bit affecting the way the hw fill the FIFO.
This may not be the final solution but should hopefully
avoid some underruns in the meantime.

v2: Apparently PIPE_CHICKEN is icl+ only

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
drivers/gpu/drm/i915/i915_reg.h | 1 +
drivers/gpu/drm/i915/intel_display.c | 6 ++++++
2 files changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index ede54fdc1676..12964b0fbc54 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -7618,6 +7618,7 @@ enum {
#define _PIPEB_CHICKEN 0x71038
#define _PIPEC_CHICKEN 0x72038
#define PER_PIXEL_ALPHA_BYPASS_EN (1 << 7)
+#define PM_FILL_MAINTAIN_DBUF_FULLNESS (1 << 0)
#define PIPE_CHICKEN(pipe) _MMIO_PIPE(pipe, _PIPEA_CHICKEN,\
_PIPEB_CHICKEN)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 5b9b9791d290..b825ceed7f1d 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3911,6 +3911,12 @@ static void icl_set_pipe_chicken(struct intel_crtc *crtc)
*/
tmp |= PER_PIXEL_ALPHA_BYPASS_EN;

+ /*
+ * W/A for underruns with linear/X-tiled with
+ * WM1+ disabled.
+ */
+ tmp |= PM_FILL_MAINTAIN_DBUF_FULLNESS;
+
I915_WRITE(PIPE_CHICKEN(pipe), tmp);
}

--
2.19.2