[Intel-gfx] [PATCH v2 6/6] drm/i915/vlv: Modifying WA 'WaDisableL3Bank2xClockGate for vlv

[sourab.gupta at intel.com]

From: Akash Goel <akash.goel at intel.com>

For disabling L3 clock gating we need to set bit 25 of MMIO
register 940c. Earlier this was being done by just writing 1
into bit 25 and resetting all other bits.
This patch modifies the routine to read-modify-write of the
register, so that the values of other bits are not destroyed.

v2: Modifying the comments and the patch commit message (Chris)

Signed-off-by: Akash Goel <akash.goel at intel.com>
Signed-off-by: Sourab Gupta <sourab.gupta at intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index c3a8554..af4bb8e 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5093,8 +5093,11 @@ static void valleyview_init_clock_gating(struct drm_device *dev)
 	I915_WRITE(GEN6_UCGCTL2,
 		   GEN6_RCZUNIT_CLOCK_GATE_DISABLE);
 
-	/* WaDisableL3Bank2xClockGate:vlv */
-	I915_WRITE(GEN7_UCGCTL4, GEN7_L3BANK2X_CLOCK_GATE_DISABLE);
+	/* WaDisableL3Bank2xClockGate:vlv
+	 * Disabling L3 clock gating- MMIO 940c[25] = 1
+	 * Set bit 25, to disable L3_BANK_2x_CLK_GATING */
+	I915_WRITE(GEN7_UCGCTL4,
+			I915_READ(GEN7_UCGCTL4) | GEN7_L3BANK2X_CLOCK_GATE_DISABLE);
 
 	I915_WRITE(MI_ARB_VLV, MI_ARB_DISPLAY_TRICKLE_FEED_DISABLE);
 
-- 
1.8.5.1