From: Ville Syrjälä<ville.syrjala@xxxxxxxxxxxxxxx>
Apparently we must yet halve the DDL drain latency from what we're
using currently. This little nugget is not in any spec, but came
down through the grapevine.
This makes the displays a bit more stable. Not quite fully stable but at
least they don't fall over immediately on driver load.
Signed-off-by: Ville Syrjälä<ville.syrjala@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_reg.h | 1 +
drivers/gpu/drm/i915/intel_pm.c | 6 +++---
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 4ee1964..d8a0205 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -4166,6 +4166,7 @@ enum skl_disp_power_wells {
#define DSPFW_PLANEA_WM1_HI_MASK (1<<0)
/* drain latency register values*/
+#define DRAIN_LATENCY_PRECISION_8 8
#define DRAIN_LATENCY_PRECISION_16 16
#define DRAIN_LATENCY_PRECISION_32 32
#define DRAIN_LATENCY_PRECISION_64 64
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 3c64810..a70bce4 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -728,8 +728,8 @@ static bool vlv_compute_drain_latency(struct drm_crtc *crtc,
entries = DIV_ROUND_UP(clock, 1000) * pixel_size;
if (IS_CHERRYVIEW(dev))
- *prec_mult = (entries > 128) ? DRAIN_LATENCY_PRECISION_32 :
- DRAIN_LATENCY_PRECISION_16;
+ *prec_mult = (entries > 32) ? DRAIN_LATENCY_PRECISION_16 :
+ DRAIN_LATENCY_PRECISION_8;
else
*prec_mult = (entries > 128) ? DRAIN_LATENCY_PRECISION_64 :
DRAIN_LATENCY_PRECISION_32;
@@ -759,7 +759,7 @@ static void vlv_update_drain_latency(struct drm_crtc *crtc)
enum pipe pipe = intel_crtc->pipe;
int plane_prec, prec_mult, plane_dl;
const int high_precision = IS_CHERRYVIEW(dev) ?
- DRAIN_LATENCY_PRECISION_32 : DRAIN_LATENCY_PRECISION_64;
The spec says that the drain latency precision are 32 and 16.
But just to be safe and have a stable environment, we further divide the
calculated DDL by 2 but precision remains the same 32 and 16.
Thanks and Regards,
Arun R Murthy
-------------------
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