drm/i915: Workaround async flip + VT-d corruption on HSW/BDW

On HSW/BDW with VT-d active the first tile row scanned out
after the first async flip of the frame often ends up corrupted.

Whether the corruption happens or not depends on the scanline
on which the async flip happens, but the behaviour seems very
consistent. Ie. the same set of scanlines (which are most scanlines)
always show the corruption. And another set of scanlines (far less
of them) never shows the corruption.

I discovered that disabling the fetch-stride stretching
feature cures the corruption. This is some kind of TLB related
prefetch thing AFAIK. We already disable it on SNB primary
planes due to a documented workaround. The hardware folks
indicated that disabling this should be fine, so let's go
with that.

And while we're here, let's document the relevant bits on all
pre-skl platforms.

Fixes: 2a636e2 ("drm/i915: Implement async flip for ivb/hsw")
Fixes: cda195f ("drm/i915: Implement async flips for bdw")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210220103303.3448-1-ville.syrjala@linux.intel.com
Reviewed-by: Karthik B S <karthik.b.s@intel.com>

drivers/gpu/drm/i915/i915_reg.h

@@ -3319,7 +3319,18 @@ static inline bool i915_mmio_reg_valid(i915_reg_t reg)
 
 #define ILK_DISPLAY_CHICKEN1	_MMIO(0x42000)
 #define   ILK_FBCQ_DIS		(1 << 22)
-#define	  ILK_PABSTRETCH_DIS	(1 << 21)
+#define   ILK_PABSTRETCH_DIS	REG_BIT(21)
+#define   ILK_SABSTRETCH_DIS	REG_BIT(20)
+#define   IVB_PRI_STRETCH_MAX_MASK	REG_GENMASK(21, 20)
+#define   IVB_PRI_STRETCH_MAX_X8	REG_FIELD_PREP(IVB_PRI_STRETCH_MAX_MASK, 0)
+#define   IVB_PRI_STRETCH_MAX_X4	REG_FIELD_PREP(IVB_PRI_STRETCH_MAX_MASK, 1)
+#define   IVB_PRI_STRETCH_MAX_X2	REG_FIELD_PREP(IVB_PRI_STRETCH_MAX_MASK, 2)
+#define   IVB_PRI_STRETCH_MAX_X1	REG_FIELD_PREP(IVB_PRI_STRETCH_MAX_MASK, 3)
+#define   IVB_SPR_STRETCH_MAX_MASK	REG_GENMASK(19, 18)
+#define   IVB_SPR_STRETCH_MAX_X8	REG_FIELD_PREP(IVB_SPR_STRETCH_MAX_MASK, 0)
+#define   IVB_SPR_STRETCH_MAX_X4	REG_FIELD_PREP(IVB_SPR_STRETCH_MAX_MASK, 1)
+#define   IVB_SPR_STRETCH_MAX_X2	REG_FIELD_PREP(IVB_SPR_STRETCH_MAX_MASK, 2)
+#define   IVB_SPR_STRETCH_MAX_X1	REG_FIELD_PREP(IVB_SPR_STRETCH_MAX_MASK, 3)
 
 
 /*
@@ -8042,6 +8053,16 @@ enum {
 
 #define _CHICKEN_PIPESL_1_A	0x420b0
 #define _CHICKEN_PIPESL_1_B	0x420b4
+#define  HSW_PRI_STRETCH_MAX_MASK	REG_GENMASK(28, 27)
+#define  HSW_PRI_STRETCH_MAX_X8		REG_FIELD_PREP(HSW_PRI_STRETCH_MAX_MASK, 0)
+#define  HSW_PRI_STRETCH_MAX_X4		REG_FIELD_PREP(HSW_PRI_STRETCH_MAX_MASK, 1)
+#define  HSW_PRI_STRETCH_MAX_X2		REG_FIELD_PREP(HSW_PRI_STRETCH_MAX_MASK, 2)
+#define  HSW_PRI_STRETCH_MAX_X1		REG_FIELD_PREP(HSW_PRI_STRETCH_MAX_MASK, 3)
+#define  HSW_SPR_STRETCH_MAX_MASK	REG_GENMASK(26, 25)
+#define  HSW_SPR_STRETCH_MAX_X8		REG_FIELD_PREP(HSW_SPR_STRETCH_MAX_MASK, 0)
+#define  HSW_SPR_STRETCH_MAX_X4		REG_FIELD_PREP(HSW_SPR_STRETCH_MAX_MASK, 1)
+#define  HSW_SPR_STRETCH_MAX_X2		REG_FIELD_PREP(HSW_SPR_STRETCH_MAX_MASK, 2)
+#define  HSW_SPR_STRETCH_MAX_X1		REG_FIELD_PREP(HSW_SPR_STRETCH_MAX_MASK, 3)
 #define  HSW_FBCQ_DIS			(1 << 22)
 #define  BDW_DPRS_MASK_VBLANK_SRD	(1 << 0)
 #define CHICKEN_PIPESL_1(pipe) _MMIO_PIPE(pipe, _CHICKEN_PIPESL_1_A, _CHICKEN_PIPESL_1_B)

drivers/gpu/drm/i915/intel_pm.c

@@ -7287,11 +7287,16 @@ static void bdw_init_clock_gating(struct drm_i915_private *dev_priv)
 	intel_uncore_write(&dev_priv->uncore, CHICKEN_PAR1_1,
 		   intel_uncore_read(&dev_priv->uncore, CHICKEN_PAR1_1) | DPA_MASK_VBLANK_SRD);
 
-	/* WaPsrDPRSUnmaskVBlankInSRD:bdw */
 	for_each_pipe(dev_priv, pipe) {
+		/* WaPsrDPRSUnmaskVBlankInSRD:bdw */
 		intel_uncore_write(&dev_priv->uncore, CHICKEN_PIPESL_1(pipe),
 			   intel_uncore_read(&dev_priv->uncore, CHICKEN_PIPESL_1(pipe)) |
 			   BDW_DPRS_MASK_VBLANK_SRD);
+
+		/* Undocumented but fixes async flip + VT-d corruption */
+		if (intel_vtd_active())
+			intel_uncore_rmw(&dev_priv->uncore, CHICKEN_PIPESL_1(pipe),
+					 HSW_PRI_STRETCH_MAX_MASK, HSW_PRI_STRETCH_MAX_X1);
 	}
 
 	/* WaVSRefCountFullforceMissDisable:bdw */
@@ -7327,11 +7332,20 @@ static void bdw_init_clock_gating(struct drm_i915_private *dev_priv)
 
 static void hsw_init_clock_gating(struct drm_i915_private *dev_priv)
 {
+	enum pipe pipe;
+
 	/* WaFbcAsynchFlipDisableFbcQueue:hsw,bdw */
 	intel_uncore_write(&dev_priv->uncore, CHICKEN_PIPESL_1(PIPE_A),
 		   intel_uncore_read(&dev_priv->uncore, CHICKEN_PIPESL_1(PIPE_A)) |
 		   HSW_FBCQ_DIS);
 
+	for_each_pipe(dev_priv, pipe) {
+		/* Undocumented but fixes async flip + VT-d corruption */
+		if (intel_vtd_active())
+			intel_uncore_rmw(&dev_priv->uncore, CHICKEN_PIPESL_1(pipe),
+					 HSW_PRI_STRETCH_MAX_MASK, HSW_PRI_STRETCH_MAX_X1);
+	}
+
 	/* This is required by WaCatErrorRejectionIssue:hsw */
 	intel_uncore_write(&dev_priv->uncore, GEN7_SQ_CHICKEN_MBCUNIT_CONFIG,
 		   intel_uncore_read(&dev_priv->uncore, GEN7_SQ_CHICKEN_MBCUNIT_CONFIG) |