diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/uapi/drm/xe_drm.h | 48 |
1 files changed, 47 insertions, 1 deletions
diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h index ab7d1b26c773..1a844fa7af8a 100644 --- a/include/uapi/drm/xe_drm.h +++ b/include/uapi/drm/xe_drm.h @@ -636,8 +636,54 @@ struct drm_xe_vm_bind_op { */ __u32 obj; + /** + * @pat_index: The platform defined @pat_index to use for this mapping. + * The index basically maps to some predefined memory attributes, + * including things like caching, coherency, compression etc. The exact + * meaning of the pat_index is platform specific and defined in the + * Bspec and PRMs. When the KMD sets up the binding the index here is + * encoded into the ppGTT PTE. + * + * For coherency the @pat_index needs to be at least 1way coherent when + * drm_xe_gem_create.cpu_caching is DRM_XE_GEM_CPU_CACHING_WB. The KMD + * will extract the coherency mode from the @pat_index and reject if + * there is a mismatch (see note below for pre-MTL platforms). + * + * Note: On pre-MTL platforms there is only a caching mode and no + * explicit coherency mode, but on such hardware there is always a + * shared-LLC (or is dgpu) so all GT memory accesses are coherent with + * CPU caches even with the caching mode set as uncached. It's only the + * display engine that is incoherent (on dgpu it must be in VRAM which + * is always mapped as WC on the CPU). However to keep the uapi somewhat + * consistent with newer platforms the KMD groups the different cache + * levels into the following coherency buckets on all pre-MTL platforms: + * + * ppGTT UC -> COH_NONE + * ppGTT WC -> COH_NONE + * ppGTT WT -> COH_NONE + * ppGTT WB -> COH_AT_LEAST_1WAY + * + * In practice UC/WC/WT should only ever used for scanout surfaces on + * such platforms (or perhaps in general for dma-buf if shared with + * another device) since it is only the display engine that is actually + * incoherent. Everything else should typically use WB given that we + * have a shared-LLC. On MTL+ this completely changes and the HW + * defines the coherency mode as part of the @pat_index, where + * incoherent GT access is possible. + * + * Note: For userptr and externally imported dma-buf the kernel expects + * either 1WAY or 2WAY for the @pat_index. + * + * For DRM_XE_VM_BIND_FLAG_NULL bindings there are no KMD restrictions + * on the @pat_index. For such mappings there is no actual memory being + * mapped (the address in the PTE is invalid), so the various PAT memory + * attributes likely do not apply. Simply leaving as zero is one + * option (still a valid pat_index). + */ + __u16 pat_index; + /** @pad: MBZ */ - __u32 pad; + __u16 pad; union { /** |