drm/shmem: add support for per object caching flags.

Add map_cached bool to drm_gem_shmem_object, to request cached mappings
on a per-object base.  Check the flag before adding writecombine to
pgprot bits.

Cc: stable@vger.kernel.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Guillaume Gardet <Guillaume.Gardet@arm.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200226154752.24328-2-kraxel@redhat.com

drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -254,11 +254,16 @@ static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
 	if (ret)
 		goto err_zero_use;
 
-	if (obj->import_attach)
+	if (obj->import_attach) {
 		shmem->vaddr = dma_buf_vmap(obj->import_attach->dmabuf);
-	else
+	} else {
+		pgprot_t prot = PAGE_KERNEL;
+
+		if (!shmem->map_cached)
+			prot = pgprot_writecombine(prot);
 		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
-				    VM_MAP, pgprot_writecombine(PAGE_KERNEL));
+				    VM_MAP, prot);
+	}
 
 	if (!shmem->vaddr) {
 		DRM_DEBUG_KMS("Failed to vmap pages\n");
@@ -540,7 +545,9 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
 	}
 
 	vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;
-	vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
+	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
+	if (!shmem->map_cached)
+		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
 	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 	vma->vm_ops = &drm_gem_shmem_vm_ops;
 

include/drm/drm_gem_shmem_helper.h

@@ -96,6 +96,11 @@ struct drm_gem_shmem_object {
 	 * The address are un-mapped when the count reaches zero.
 	 */
 	unsigned int vmap_use_count;
+
+	/**
+	 * @map_cached: map object cached (instead of using writecombine).
+	 */
+	bool map_cached;
 };
 
 #define to_drm_gem_shmem_obj(obj) \