[PATCH 1/2] drm/shmem: Use cached mappings by default

[Thomas Zimmermann]

SHMEM-buffer backing storage is allocated from system memory; which is
typically cachable. Currently, only virtio uses cachable mappings; udl
uses its own vmap/mmap implementation for cachable mappings. Other
drivers default to writecombine mappings.

Use cached mappings by default. The exception is pages imported via
dma-buf. DMA memory is usually not cached.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c  | 6 ++++--
 drivers/gpu/drm/virtio/virtgpu_object.c | 1 -
 include/drm/drm_gem_shmem_helper.h      | 4 ++--
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index df31e5782eed1..1ce90325dfa31 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -259,7 +259,7 @@ static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
 	} else {
 		pgprot_t prot = PAGE_KERNEL;
 
-		if (!shmem->map_cached)
+		if (shmem->map_wc)
 			prot = pgprot_writecombine(prot);
 		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
 				    VM_MAP, prot);
@@ -546,7 +546,7 @@ 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 = vm_get_page_prot(vma->vm_flags);
-	if (!shmem->map_cached)
+	if (shmem->map_wc)
 		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
 	vma->vm_ops = &drm_gem_shmem_vm_ops;
 
@@ -664,6 +664,8 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
 	if (IS_ERR(shmem))
 		return ERR_CAST(shmem);
 
+	shmem->map_wc = false; /* dma-buf mappings use writecombine */
+
 	shmem->pages = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
 	if (!shmem->pages) {
 		ret = -ENOMEM;
diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
index 6ccbd01cd888c..80ba6b2b61668 100644
--- a/drivers/gpu/drm/virtio/virtgpu_object.c
+++ b/drivers/gpu/drm/virtio/virtgpu_object.c
@@ -132,7 +132,6 @@ struct drm_gem_object *virtio_gpu_create_object(struct drm_device *dev,
 
 	dshmem = &shmem->base.base;
 	dshmem->base.funcs = &virtio_gpu_shmem_funcs;
-	dshmem->map_cached = true;
 	return &dshmem->base;
 }
 
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 294b2931c4cc0..a5bc082a77c48 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -98,9 +98,9 @@ struct drm_gem_shmem_object {
 	unsigned int vmap_use_count;
 
 	/**
-	 * @map_cached: map object cached (instead of using writecombine).
+	 * @map_wc: map object using writecombine (instead of cached).
 	 */
-	bool map_cached;
+	bool map_wc;
 };
 
 #define to_drm_gem_shmem_obj(obj) \
-- 
2.26.2