diff options
Diffstat (limited to 'include/uapi/drm/i915_drm.h')
| -rw-r--r-- | include/uapi/drm/i915_drm.h | 22 |
1 files changed, 22 insertions, 0 deletions
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; /* |