[PATCH 1/2] drm/i915: Apply B-spec mandated workaround for read flushes on Ironlake.

[Eric Anholt <eric@anholt.net>]

This is not known to fix any particular bugs we have, but the spec
says to do it, and the BIOS hadn't already set it up on my system.

Signed-off-by: Eric Anholt <eric@anholt.net>
---
 drivers/gpu/drm/i915/i915_reg.h      |   13 +++++++++++++
 drivers/gpu/drm/i915/intel_display.c |    6 ++++++
 2 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 25ed911..f338499 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -306,6 +306,19 @@
 #define NOPID		0x02094
 #define HWSTAM		0x02098
 
+/* GM45+ chicken bits -- debug workaround bits that may be required
+ * for various sorts of correct behavior.  The top 16 bits of each are
+ * the enables for writing to the corresponding low bit.
+ */
+#define _3D_CHICKEN	0x02084
+#define _3D_CHICKEN2	0x0208c
+/* Disables pipelining of read flushes past the SF-WIZ interface.
+ * Required on all Ironlake steppings according to the B-Spec, but the
+ * particular danger of not doing so is not specified.
+ */
+# define _3D_CHICKEN2_WM_READ_PIPELINED			(1 << 14)
+#define _3D_CHICKEN3	0x02090
+
 #define MI_MODE		0x0209c
 # define VS_TIMER_DISPATCH				(1 << 6)
 # define MI_FLUSH_ENABLE				(1 << 11)
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 48d8fd6..360f17d 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5812,6 +5812,12 @@ void intel_init_clock_gating(struct drm_device *dev)
 				   ILK_DPFC_DIS2 |
 				   ILK_CLK_FBC);
 		}
+
+		if (IS_GEN5(dev)) {
+			I915_WRITE(_3D_CHICKEN2,
+				   _3D_CHICKEN2_WM_READ_PIPELINED << 16 |
+				   _3D_CHICKEN2_WM_READ_PIPELINED);
+		}
 		return;
 	} else if (IS_G4X(dev)) {
 		uint32_t dspclk_gate;
-- 
1.7.2.3