[Intel-gfx] [PATCH] drm/i915: vlv: W/a for hotplug/manual VGA detection

[Imre Deak]

At least on my VLV stepping VGA detection doesn't work in certain cases.
One such case is when all pipes are off and VGA is plugged in. Another
case reported by Joonas Lahtinen (also on the same stepping) is booting
with VGA disconnected where we incorrectly report that VGA is connected.
At least in the first case writing the FORCE bit in the ADPA reg will
get stuck, i.e. the detection never completes.

Both cases seem to be solved by disabling DPIO clock gating based on the
PSR state. As I haven't found any trace that this would be a known
issue, I can only speculate that both the DPIO HW block and the HW
block responsible for VGA detection uses the same clock source which gets
gated even though PSR is inactive.

I haven't measured if and how this change affects our power savings.

Reported-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h | 3 +++
 drivers/gpu/drm/i915/intel_pm.c | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 849e595..9981d21 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1447,6 +1447,9 @@
 # define I965_FT_CLOCK_GATE_DISABLE		(1 << 1)
 # define I965_DM_CLOCK_GATE_DISABLE		(1 << 0)
 
+#define DPPSR_CGDIS_VLV                (dev_priv->info->display_mmio_offset + 0x6204)
+# define DPIOUNIT_PSR_CLOCK_GATING_DISABLE     (1 << 6)
+
 #define RENCLK_GATE_D2		0x6208
 #define VF_UNIT_CLOCK_GATE_DISABLE		(1 << 9)
 #define GS_UNIT_CLOCK_GATE_DISABLE		(1 << 7)
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 365545f..7f373e9 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5430,6 +5430,11 @@ static void valleyview_init_clock_gating(struct drm_device *dev)
 
 	I915_WRITE(DSPCLK_GATE_D, VRHUNIT_CLOCK_GATE_DISABLE);
 
+	/* Wa to make VGA hotplug and manual detection work. */
+	val = I915_READ(DPPSR_CGDIS_VLV);
+	val |= DPIOUNIT_PSR_CLOCK_GATING_DISABLE;
+	I915_WRITE(DPIOUNIT_PSR_CLOCK_GATING_DISABLE, val);
+
 	/* WaDisableEarlyCull:vlv */
 	I915_WRITE(_3D_CHICKEN3,
 		   _MASKED_BIT_ENABLE(_3D_CHICKEN_SF_DISABLE_OBJEND_CULL));
-- 
1.8.4