drm/i915: Enable provoking vertex fix on Gen9 systems.

The SF and clipper units mishandle the provoking vertex in some cases,
which can cause misrendering with shaders that use flat shaded inputs.

There are chicken bits in 3D_CHICKEN3 (for SF) and FF_SLICE_CHICKEN
(for the clipper) that work around the issue. These registers are
unfortunately not part of the logical context (even the power context),
and so we must reload them every time we start executing in a context.

Bugzilla: https://bugs.freedesktop.org/103047
Signed-off-by: Kenneth Graunke <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Reviewed-by: Joonas Lahtinen <[e-mail]>
Cc: [e-mail]

drivers/gpu/drm/i915/i915_reg.h

···
 #define _3D_CHICKEN	_MMIO(0x2084)
 #define  _3D_CHICKEN_HIZ_PLANE_DISABLE_MSAA_4X_SNB	(1 << 10)
 #define _3D_CHICKEN2	_MMIO(0x208c)
+
+#define FF_SLICE_CHICKEN	_MMIO(0x2088)
+#define  FF_SLICE_CHICKEN_CL_PROVOKING_VERTEX_FIX	(1 << 1)
+
 /* 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	_MMIO(0x2090)
+#define  _3D_CHICKEN_SF_PROVOKING_VERTEX_FIX		(1 << 12)
 #define  _3D_CHICKEN_SF_DISABLE_OBJEND_CULL		(1 << 10)
 #define  _3D_CHICKEN3_AA_LINE_QUALITY_FIX_ENABLE	(1 << 5)
 #define  _3D_CHICKEN3_SF_DISABLE_FASTCLIP_CULL		(1 << 5)

drivers/gpu/drm/i915/intel_lrc.c

···
 	/* WaFlushCoherentL3CacheLinesAtContextSwitch:skl,bxt,glk */
 	batch = gen8_emit_flush_coherentl3_wa(engine, batch);
 
+	*batch++ = MI_LOAD_REGISTER_IMM(3);
+
 	/* WaDisableGatherAtSetShaderCommonSlice:skl,bxt,kbl,glk */
-	*batch++ = MI_LOAD_REGISTER_IMM(1);
 	*batch++ = i915_mmio_reg_offset(COMMON_SLICE_CHICKEN2);
 	*batch++ = _MASKED_BIT_DISABLE(
 			GEN9_DISABLE_GATHER_AT_SET_SHADER_COMMON_SLICE);
+
+	/* BSpec: 11391 */
+	*batch++ = i915_mmio_reg_offset(FF_SLICE_CHICKEN);
+	*batch++ = _MASKED_BIT_ENABLE(FF_SLICE_CHICKEN_CL_PROVOKING_VERTEX_FIX);
+
+	/* BSpec: 11299 */
+	*batch++ = i915_mmio_reg_offset(_3D_CHICKEN3);
+	*batch++ = _MASKED_BIT_ENABLE(_3D_CHICKEN_SF_PROVOKING_VERTEX_FIX);
+
 	*batch++ = MI_NOOP;
 
 	/* WaClearSlmSpaceAtContextSwitch:kbl */