drm/i915: Enable CB tuning of the Display PLL
Magic numbers from the specs. This is supposed to allow the PLL some
variance to improve jitter performance and VCO headroom across
manufacturing and environmental variations.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index e3b8d0d..f2aa76b 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3857,6 +3857,22 @@
reduced_clock.m2;
}
+ /* Enable autotuning of the PLL clock (if permissible) */
+ if (HAS_PCH_SPLIT(dev)) {
+ int factor = 21;
+
+ if (is_lvds) {
+ if ((dev_priv->lvds_use_ssc &&
+ dev_priv->lvds_ssc_freq == 100) ||
+ (I915_READ(PCH_LVDS) & LVDS_CLKB_POWER_MASK) == LVDS_CLKB_POWER_UP)
+ factor = 25;
+ } else if (is_sdvo && is_tv)
+ factor = 20;
+
+ if (clock.m1 < factor * clock.n)
+ fp |= FP_CB_TUNE;
+ }
+
dpll = 0;
if (!HAS_PCH_SPLIT(dev))
dpll = DPLL_VGA_MODE_DIS;
@@ -4071,7 +4087,6 @@
}
if (!has_edp_encoder || intel_encoder_is_pch_edp(&has_edp_encoder->base)) {
- I915_WRITE(fp_reg, fp);
I915_WRITE(dpll_reg, dpll);
/* Wait for the clocks to stabilize. */