[igt-dev] [PATCH i-g-t v8 01/15] drm-uapi/xe_drm: sync to get pat and coherency bits

[Matthew Auld <matthew.auld@intel.com>]

Grab the PAT & coherency uapi additions.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Pallavi Mishra <pallavi.mishra@intel.com>
Reviewed-by: Pallavi Mishra <pallavi.mishra@intel.com>
---
 include/drm-uapi/xe_drm.h | 61 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 59 insertions(+), 2 deletions(-)

diff --git a/include/drm-uapi/xe_drm.h b/include/drm-uapi/xe_drm.h
index 6ff1106e4..d7893642b 100644
--- a/include/drm-uapi/xe_drm.h
+++ b/include/drm-uapi/xe_drm.h
@@ -548,8 +548,25 @@ struct drm_xe_gem_create {
 	 */
 	__u32 handle;
 
+	/**
+	 * @cpu_caching: The CPU caching mode to select for this object. If
+	 * mmaping the object the mode selected here will also be used.
+	 *
+	 * Supported values:
+	 *
+	 * DRM_XE_GEM_CPU_CACHING_WB: Allocate the pages with write-back
+	 * caching.  On iGPU this can't be used for scanout surfaces. Currently
+	 * not allowed for objects placed in VRAM.
+	 *
+	 * DRM_XE_GEM_CPU_CACHING_WC: Allocate the pages as write-combined. This
+	 * is uncached. Scanout surfaces should likely use this. All objects
+	 * that can be placed in VRAM must use this.
+	 */
+#define DRM_XE_GEM_CPU_CACHING_WB                      1
+#define DRM_XE_GEM_CPU_CACHING_WC                      2
+	__u16 cpu_caching;
 	/** @pad: MBZ */
-	__u32 pad;
+	__u16 pad;
 
 	/** @reserved: Reserved */
 	__u64 reserved[2];
@@ -626,8 +643,48 @@ 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.
+	 */
+	__u16 pat_index;
+
 	/** @pad: MBZ */
-	__u32 pad;
+	__u16 pad;
 
 	union {
 		/**
-- 
2.41.0