2 files changed, 23 insertions, 0 deletions

diff --git a/include/drm/i915_pciids.h b/include/drm/i915_pciids.h
index fbf5cfc9b352..fd965ffbb92e 100644
--- a/include/drm/i915_pciids.h
+++ b/include/drm/i915_pciids.h
@@ -386,6 +386,7 @@
         INTEL_VGA_DEVICE(0x3E91, info), /* SRV GT2 */ \
         INTEL_VGA_DEVICE(0x3E92, info), /* SRV GT2 */ \
         INTEL_VGA_DEVICE(0x3E96, info), /* SRV GT2 */ \
+        INTEL_VGA_DEVICE(0x3E98, info), /* SRV GT2 */ \
         INTEL_VGA_DEVICE(0x3E9A, info)  /* SRV GT2 */
 
 /* CFL H */
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 7f5634ce8e88..a4446f452040 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -529,6 +529,28 @@ typedef struct drm_i915_irq_wait {
  */
 #define I915_PARAM_CS_TIMESTAMP_FREQUENCY 51
 
+/*
+ * Once upon a time we supposed that writes through the GGTT would be
+ * immediately in physical memory (once flushed out of the CPU path). However,
+ * on a few different processors and chipsets, this is not necessarily the case
+ * as the writes appear to be buffered internally. Thus a read of the backing
+ * storage (physical memory) via a different path (with different physical tags
+ * to the indirect write via the GGTT) will see stale values from before
+ * the GGTT write. Inside the kernel, we can for the most part keep track of
+ * the different read/write domains in use (e.g. set-domain), but the assumption
+ * of coherency is baked into the ABI, hence reporting its true state in this
+ * parameter.
+ *
+ * Reports true when writes via mmap_gtt are immediately visible following an
+ * lfence to flush the WCB.
+ *
+ * Reports false when writes via mmap_gtt are indeterminately delayed in an in
+ * internal buffer and are _not_ immediately visible to third parties accessing
+ * directly via mmap_cpu/mmap_wc. Use of mmap_gtt as part of an IPC
+ * communications channel when reporting false is strongly disadvised.
+ */
+#define I915_PARAM_MMAP_GTT_COHERENT    52
+
 typedef struct drm_i915_getparam {
         __s32 param;
         /*