drm/xe/xe_migrate: Use NULL 1G PTE mapped at 255GiB VA for ccs clear

Get rid of the cleared bo, instead use null 1G PTE mapped at 255GiB
offset, this can be used for both dgfx and igfx.

v2:
 - Remove xe_migrate::cleared_bo.
 - Add a comment for NULL mapping.(Thomas)

Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_migrate.c

@@ -46,16 +46,12 @@ struct xe_migrate {
 	struct mutex job_mutex;
 	/** @pt_bo: Page-table buffer object. */
 	struct xe_bo *pt_bo;
-	/**
-	 * @cleared_bo: Zeroed out bo used as a source for CCS metadata clears
-	 */
-	struct xe_bo *cleared_bo;
 	/** @batch_base_ofs: VM offset of the migration batch buffer */
 	u64 batch_base_ofs;
 	/** @usm_batch_base_ofs: VM offset of the usm batch buffer */
 	u64 usm_batch_base_ofs;
-	/** @cleared_vram_ofs: VM offset of @cleared_bo. */
-	u64 cleared_vram_ofs;
+	/** @cleared_mem_ofs: VM offset of @cleared_bo. */
+	u64 cleared_mem_ofs;
 	/**
 	 * @fence: dma-fence representing the last migration job batch.
 	 * Protected by @job_mutex.
@@ -93,13 +89,9 @@ static void xe_migrate_fini(struct drm_device *dev, void *arg)
 
 	xe_vm_lock(m->q->vm, false);
 	xe_bo_unpin(m->pt_bo);
-	if (m->cleared_bo)
-		xe_bo_unpin(m->cleared_bo);
 	xe_vm_unlock(m->q->vm);
 
 	dma_fence_put(m->fence);
-	if (m->cleared_bo)
-		xe_bo_put(m->cleared_bo);
 	xe_bo_put(m->pt_bo);
 	drm_suballoc_manager_fini(&m->vm_update_sa);
 	mutex_destroy(&m->job_mutex);
@@ -125,41 +117,6 @@ static u64 xe_migrate_vram_ofs(struct xe_device *xe, u64 addr)
 	return addr + (256ULL << xe_pt_shift(2));
 }
 
-/*
- * For flat CCS clearing we need a cleared chunk of memory to copy from,
- * since the CCS clearing mode of XY_FAST_COLOR_BLT appears to be buggy
- * (it clears on only 14 bytes in each chunk of 16).
- * If clearing the main surface one can use the part of the main surface
- * already cleared, but for clearing as part of copying non-compressed
- * data out of system memory, we don't readily have a cleared part of
- * VRAM to copy from, so create one to use for that case.
- */
-static int xe_migrate_create_cleared_bo(struct xe_migrate *m, struct xe_vm *vm)
-{
-	struct xe_tile *tile = m->tile;
-	struct xe_device *xe = vm->xe;
-	size_t cleared_size;
-	u64 vram_addr;
-
-	if (!xe_device_has_flat_ccs(xe))
-		return 0;
-
-	cleared_size = xe_device_ccs_bytes(xe, MAX_PREEMPTDISABLE_TRANSFER);
-	cleared_size = PAGE_ALIGN(cleared_size);
-	m->cleared_bo = xe_bo_create_pin_map(xe, tile, vm, cleared_size,
-					     ttm_bo_type_kernel,
-					     XE_BO_CREATE_VRAM_IF_DGFX(tile) |
-					     XE_BO_CREATE_PINNED_BIT);
-	if (IS_ERR(m->cleared_bo))
-		return PTR_ERR(m->cleared_bo);
-
-	xe_map_memset(xe, &m->cleared_bo->vmap, 0, 0x00, cleared_size);
-	vram_addr = xe_bo_addr(m->cleared_bo, 0, XE_PAGE_SIZE);
-	m->cleared_vram_ofs = xe_migrate_vram_ofs(xe, vram_addr);
-
-	return 0;
-}
-
 static int xe_migrate_prepare_vm(struct xe_tile *tile, struct xe_migrate *m,
 				 struct xe_vm *vm)
 {
@@ -170,7 +127,6 @@ static int xe_migrate_prepare_vm(struct xe_tile *tile, struct xe_migrate *m,
 	u32 map_ofs, level, i;
 	struct xe_bo *bo, *batch = tile->mem.kernel_bb_pool->bo;
 	u64 entry;
-	int ret;
 
 	/* Can't bump NUM_PT_SLOTS too high */
 	BUILD_BUG_ON(NUM_PT_SLOTS > SZ_2M/XE_PAGE_SIZE);
@@ -190,12 +146,6 @@ static int xe_migrate_prepare_vm(struct xe_tile *tile, struct xe_migrate *m,
 	if (IS_ERR(bo))
 		return PTR_ERR(bo);
 
-	ret = xe_migrate_create_cleared_bo(m, vm);
-	if (ret) {
-		xe_bo_put(bo);
-		return ret;
-	}
-
 	entry = vm->pt_ops->pde_encode_bo(bo, bo->size - XE_PAGE_SIZE, pat_index);
 	xe_pt_write(xe, &vm->pt_root[id]->bo->vmap, 0, entry);
 
@@ -265,6 +215,13 @@ static int xe_migrate_prepare_vm(struct xe_tile *tile, struct xe_migrate *m,
 			  (i + 1) * 8, u64, entry);
 	}
 
+	/* Set up a 1GiB NULL mapping at 255GiB offset. */
+	level = 2;
+	xe_map_wr(xe, &bo->vmap, map_ofs + XE_PAGE_SIZE * level + 255 * 8, u64,
+		  vm->pt_ops->pte_encode_addr(xe, 0, pat_index, level, IS_DGFX(xe), 0)
+		  | XE_PTE_NULL);
+	m->cleared_mem_ofs = (255ULL << xe_pt_shift(level));
+
 	/* Identity map the entire vram at 256GiB offset */
 	if (IS_DGFX(xe)) {
 		u64 pos, ofs, flags;
@@ -618,7 +575,7 @@ static u32 xe_migrate_ccs_copy(struct xe_migrate *m,
 		 * Otherwise if the bo doesn't have any CCS metadata attached,
 		 * we still need to clear it for security reasons.
 		 */
-		u64 ccs_src_ofs =  src_is_vram ? src_ofs : m->cleared_vram_ofs;
+		u64 ccs_src_ofs =  src_is_vram ? src_ofs : m->cleared_mem_ofs;
 
 		emit_copy_ccs(gt, bb,
 			      dst_ofs, true,
@@ -1006,7 +963,7 @@ struct dma_fence *xe_migrate_clear(struct xe_migrate *m,
 			   clear_vram);
 		if (xe_device_has_flat_ccs(xe) && clear_vram) {
 			emit_copy_ccs(gt, bb, clear_L0_ofs, true,
-				      m->cleared_vram_ofs, false, clear_L0);
+				      m->cleared_mem_ofs, false, clear_L0);
 			flush_flags = MI_FLUSH_DW_CCS;
 		}