[Mesa-dev] [PATCHv2] i965/gen9: Use custom MOCS entries set up by the kernel.

Francisco Jerez currojerez at riseup.net
Tue Jul 7 12:21:28 PDT 2015

Instead of relying on hardware defaults the i915 kernel driver is
going program custom MOCS tables system-wide on Gen9 hardware.  The
"WT" entry previously used for renderbuffers had a number of problems:
It disabled caching on eLLC, it used a reserved L3 cacheability
setting, and it used to override the PTE controls making renderbuffers
always WT on LLC regardless of the kernel's setting.  Instead use an
entry from the new MOCS tables with parameters: TC=LLC/eLLC, LeCC=PTE,

The "WB" entry previously used for anything other than renderbuffers
has moved to a different index in the new MOCS tables but it should
have the same caching semantics as the old entry.

Even though the corresponding kernel change ("drm/i915: Added
Programming of the MOCS") is in a way an ABI break it doesn't seem
necessary to check that the kernel is recent enough because the change
should only affect Gen9 which is still unreleased hardware.

v2: Update MOCS values for the new Android-incompatible tables
    introduced in v7 of the kernel patch.

Cc: 10.6 <mesa-stable at lists.freedesktop.org>
 src/mesa/drivers/dri/i965/brw_defines.h        | 11 ++++++-----
 src/mesa/drivers/dri/i965/gen8_surface_state.c |  3 +--
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
index 66b9abc..8ab8d62 100644
--- a/src/mesa/drivers/dri/i965/brw_defines.h
+++ b/src/mesa/drivers/dri/i965/brw_defines.h
@@ -2491,12 +2491,13 @@ enum brw_wm_barycentric_interp_mode {
 #define BDW_MOCS_WT  0x58
 #define BDW_MOCS_PTE 0x18
-/* Skylake: MOCS is now an index into an array of 64 different configurable
- * cache settings.  We still use only either write-back or write-through; and
- * rely on the documented default values.
+/* Skylake: MOCS is now an index into an array of 62 different caching
+ * configurations programmed by the kernel.
-#define SKL_MOCS_WB (0b001001 << 1)
-#define SKL_MOCS_WT (0b000101 << 1)
+/* TC=LLC/eLLC, LeCC=WB, LRUM=3, L3CC=WB */
+#define SKL_MOCS_WB  (2 << 1)
+#define SKL_MOCS_PTE (1 << 1)
 #define MEDIA_VFE_STATE                         0x7000
 /* GEN7 DW2, GEN8+ DW3 */
diff --git a/src/mesa/drivers/dri/i965/gen8_surface_state.c b/src/mesa/drivers/dri/i965/gen8_surface_state.c
index bd3eb00..dfaf762 100644
--- a/src/mesa/drivers/dri/i965/gen8_surface_state.c
+++ b/src/mesa/drivers/dri/i965/gen8_surface_state.c
@@ -401,8 +401,7 @@ gen8_update_renderbuffer_surface(struct brw_context *brw,
       irb->mt_layer : (irb->mt_layer / MAX2(mt->num_samples, 1));
    GLenum gl_target =
       rb->TexImage ? rb->TexImage->TexObject->Target : GL_TEXTURE_2D;
-   /* FINISHME: Use PTE MOCS on Skylake. */
-   uint32_t mocs = brw->gen >= 9 ? SKL_MOCS_WT : BDW_MOCS_PTE;
+   uint32_t mocs = brw->gen >= 9 ? SKL_MOCS_PTE : BDW_MOCS_PTE;

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