[Intel-gfx] [PATCH] drm/i915: Wait for the clocks to stabilise before updating PLLs

[Chris Wilson]

Cc: Ben Widawsky <ben at bwidawsk.net>
Cc: Jesse Barnes <jbarnes at virtuousgeek.org>
---
 drivers/gpu/drm/i915/intel_display.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index d5aa2d2..b97112c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2845,11 +2845,14 @@ found:
 	DRM_DEBUG_DRIVER("using pll %d for pipe %d\n", i, intel_crtc->pipe);
 prepare: /* separate function? */
 	DRM_DEBUG_DRIVER("switching PLL %x off\n", pll->pll_reg);
-	I915_WRITE(pll->fp0_reg, fp);
-	I915_WRITE(pll->pll_reg, dpll & ~DPLL_VCO_ENABLE);
 
+	/* Wait for the clocks to stabilize before rewriting the regs */
+	I915_WRITE(pll->pll_reg, dpll & ~DPLL_VCO_ENABLE);
 	POSTING_READ(pll->pll_reg);
 	udelay(150);
+
+	I915_WRITE(pll->fp0_reg, fp);
+	I915_WRITE(pll->pll_reg, dpll & ~DPLL_VCO_ENABLE);
 	pll->on = false;
 	return pll;
 }
-- 
1.7.10