[PATCH v2 1/2] drm/shmem: add support for per object caching attributes

[Gerd Hoffmann]

Add caching field to drm_gem_shmem_object to specify the cachine
attributes for mappings.  Add helper function to tweak pgprot
accordingly.  Switch vmap and mmap functions to the new helper.

Set caching to write-combine when creating the object so behavior
doesn't change by default.  Drivers can override that later if
needed.

Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
---
 include/drm/drm_gem_shmem_helper.h     | 12 ++++++++++++
 drivers/gpu/drm/drm_gem_shmem_helper.c | 24 +++++++++++++++++++++---
 2 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 6748379a0b44..9d6e02c6205f 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -17,6 +17,11 @@ struct drm_mode_create_dumb;
 struct drm_printer;
 struct sg_table;
 
+enum drm_gem_shmem_caching {
+	DRM_GEM_SHMEM_CACHED = 1,
+	DRM_GEM_SHMEM_WC,
+};
+
 /**
  * struct drm_gem_shmem_object - GEM object backed by shmem
  */
@@ -83,6 +88,11 @@ struct drm_gem_shmem_object {
 	 * The address are un-mapped when the count reaches zero.
 	 */
 	unsigned int vmap_use_count;
+
+	/**
+	 * @caching: caching attributes for mappings.
+	 */
+	enum drm_gem_shmem_caching caching;
 };
 
 #define to_drm_gem_shmem_obj(obj) \
@@ -130,6 +140,8 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
 
 struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_object *obj);
 
+pgprot_t drm_gem_shmem_caching(struct drm_gem_shmem_object *shmem, pgprot_t prot);
+
 /**
  * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
  *
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index a421a2eed48a..5bb94e130a50 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -76,6 +76,7 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
 	mutex_init(&shmem->pages_lock);
 	mutex_init(&shmem->vmap_lock);
 	INIT_LIST_HEAD(&shmem->madv_list);
+	shmem->caching = DRM_GEM_SHMEM_WC;
 
 	/*
 	 * Our buffers are kept pinned, so allocating them
@@ -256,9 +257,11 @@ static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
 
 	if (obj->import_attach)
 		shmem->vaddr = dma_buf_vmap(obj->import_attach->dmabuf);
-	else
+	else {
+		pgprot_t prot = drm_gem_shmem_caching(shmem, PAGE_KERNEL);
 		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 +543,8 @@ 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);
+	vma->vm_page_prot = drm_gem_shmem_caching(shmem, vma->vm_page_prot);
 	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 	vma->vm_ops = &drm_gem_shmem_vm_ops;
 
@@ -683,3 +687,17 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
 	return ERR_PTR(ret);
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);
+
+pgprot_t drm_gem_shmem_caching(struct drm_gem_shmem_object *shmem, pgprot_t prot)
+{
+	switch (shmem->caching) {
+	case DRM_GEM_SHMEM_CACHED:
+		return prot;
+	case DRM_GEM_SHMEM_WC:
+		return pgprot_writecombine(prot);
+	default:
+		WARN_ON_ONCE(1);
+		return prot;
+	}
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_caching);
-- 
2.18.1