[PATCH] drm: gem: add an option for supporting the dma-coherent hardware.

[Sui Jingfeng]

The single map_noncoherent member of struct drm_gem_dma_object may not
sufficient for describing the backing memory of the GEM buffer object.

Especially on dma-coherent systems, the backing memory is both cached
coherent for multi-core CPUs and dma-coherent for peripheral device.
Say architectures like X86-64, LoongArch64, Loongson Mips64, etc.

Whether a peripheral device is dma-coherent or not can be
implementation-dependent. The single map_noncoherent option is not enough
to reflect real hardware anymore. For example, the Loongson LS3A4000 CPU
and LS2K2000/LS2K1000 SoC, peripheral device of such hardware platform
allways snoop CPU's cache. Doing the allocation with dma_alloc_coherent
function is preferred. The return buffer is cached, it should not using
the default write-combine mapping. While with the current implement, there
no way to tell the drm core to reflect this.

This patch adds cached and coherent members to struct drm_gem_dma_object.
which allow driver implements to inform the core. Introducing new mappings
while keeping the original default behavior unchanged.

Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
---
 drivers/gpu/drm/drm_fb_dma_helper.c       | 11 +++++------
 drivers/gpu/drm/drm_fbdev_dma.c           |  2 +-
 drivers/gpu/drm/drm_gem_dma_helper.c      | 20 ++++++++++++++++----
 drivers/gpu/drm/ingenic/ingenic-drm-drv.c |  5 ++++-
 drivers/gpu/drm/rcar-du/Kconfig           |  2 --
 drivers/gpu/drm/rcar-du/rcar_du_kms.c     |  4 +++-
 include/drm/drm_gem_dma_helper.h          |  7 +++++--
 7 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_dma_helper.c b/drivers/gpu/drm/drm_fb_dma_helper.c
index 3b535ad1b07c..93ff05041192 100644
--- a/drivers/gpu/drm/drm_fb_dma_helper.c
+++ b/drivers/gpu/drm/drm_fb_dma_helper.c
@@ -106,16 +106,15 @@ dma_addr_t drm_fb_dma_get_gem_addr(struct drm_framebuffer *fb,
 EXPORT_SYMBOL_GPL(drm_fb_dma_get_gem_addr);
 
 /**
- * drm_fb_dma_sync_non_coherent - Sync GEM object to non-coherent backing
- *	memory
+ * drm_fb_dma_sync_non_coherent - Sync GEM object to cached backing memory
  * @drm: DRM device
  * @old_state: Old plane state
  * @state: New plane state
  *
  * This function can be used by drivers that use damage clips and have
- * DMA GEM objects backed by non-coherent memory. Calling this function
- * in a plane's .atomic_update ensures that all the data in the backing
- * memory have been written to RAM.
+ * DMA GEM objects backed by cached memory. Calling this function in a
+ * plane's .atomic_update ensures that all the data in the backing memory
+ * have been written to RAM.
  */
 void drm_fb_dma_sync_non_coherent(struct drm_device *drm,
 				  struct drm_plane_state *old_state,
@@ -131,7 +130,7 @@ void drm_fb_dma_sync_non_coherent(struct drm_device *drm,
 
 	for (i = 0; i < finfo->num_planes; i++) {
 		dma_obj = drm_fb_dma_get_gem_obj(state->fb, i);
-		if (!dma_obj->map_noncoherent)
+		if (dma_obj->cached && dma_obj->coherent)
 			continue;
 
 		daddr = drm_fb_dma_get_gem_addr(state->fb, state, i);
diff --git a/drivers/gpu/drm/drm_fbdev_dma.c b/drivers/gpu/drm/drm_fbdev_dma.c
index d86773fa8ab0..49fe9b284cc8 100644
--- a/drivers/gpu/drm/drm_fbdev_dma.c
+++ b/drivers/gpu/drm/drm_fbdev_dma.c
@@ -131,7 +131,7 @@ static int drm_fbdev_dma_helper_fb_probe(struct drm_fb_helper *fb_helper,
 
 	/* screen */
 	info->flags |= FBINFO_VIRTFB; /* system memory */
-	if (dma_obj->map_noncoherent)
+	if (dma_obj->cached)
 		info->flags |= FBINFO_READS_FAST; /* signal caching */
 	info->screen_size = sizes->surface_height * fb->pitches[0];
 	info->screen_buffer = map.vaddr;
diff --git a/drivers/gpu/drm/drm_gem_dma_helper.c b/drivers/gpu/drm/drm_gem_dma_helper.c
index 870b90b78bc4..dec1d512bdf1 100644
--- a/drivers/gpu/drm/drm_gem_dma_helper.c
+++ b/drivers/gpu/drm/drm_gem_dma_helper.c
@@ -93,7 +93,11 @@ __drm_gem_dma_create(struct drm_device *drm, size_t size, bool private)
 		drm_gem_private_object_init(drm, gem_obj, size);
 
 		/* Always use writecombine for dma-buf mappings */
-		dma_obj->map_noncoherent = false;
+		/* FIXME: This is not always true, on some dma coherent system,
+		 * cached mappings should be preferred over writecombine
+		 */
+		dma_obj->cached = false;
+		dma_obj->coherent = false;
 	} else {
 		ret = drm_gem_object_init(drm, gem_obj, size);
 	}
@@ -143,7 +147,11 @@ struct drm_gem_dma_object *drm_gem_dma_create(struct drm_device *drm,
 	if (IS_ERR(dma_obj))
 		return dma_obj;
 
-	if (dma_obj->map_noncoherent) {
+	if (dma_obj->cached && dma_obj->coherent) {
+		dma_obj->vaddr = dma_alloc_coherent(drm->dev, size,
+						    &dma_obj->dma_addr,
+						    GFP_KERNEL | __GFP_NOWARN);
+	} else if (dma_obj->cached && !dma_obj->coherent) {
 		dma_obj->vaddr = dma_alloc_noncoherent(drm->dev, size,
 						       &dma_obj->dma_addr,
 						       DMA_TO_DEVICE,
@@ -153,6 +161,7 @@ struct drm_gem_dma_object *drm_gem_dma_create(struct drm_device *drm,
 					      &dma_obj->dma_addr,
 					      GFP_KERNEL | __GFP_NOWARN);
 	}
+
 	if (!dma_obj->vaddr) {
 		drm_dbg(drm, "failed to allocate buffer with size %zu\n",
 			 size);
@@ -233,7 +242,10 @@ void drm_gem_dma_free(struct drm_gem_dma_object *dma_obj)
 			dma_buf_vunmap_unlocked(gem_obj->import_attach->dmabuf, &map);
 		drm_prime_gem_destroy(gem_obj, dma_obj->sgt);
 	} else if (dma_obj->vaddr) {
-		if (dma_obj->map_noncoherent)
+		if (dma_obj->cached && dma_obj->coherent)
+			dma_free_coherent(gem_obj->dev->dev, dma_obj->base.size,
+					  dma_obj->vaddr, dma_obj->dma_addr);
+		else if (dma_obj->cached && !dma_obj->coherent)
 			dma_free_noncoherent(gem_obj->dev->dev, dma_obj->base.size,
 					     dma_obj->vaddr, dma_obj->dma_addr,
 					     DMA_TO_DEVICE);
@@ -532,7 +544,7 @@ int drm_gem_dma_mmap(struct drm_gem_dma_object *dma_obj, struct vm_area_struct *
 	vma->vm_pgoff -= drm_vma_node_start(&obj->vma_node);
 	vm_flags_mod(vma, VM_DONTEXPAND, VM_PFNMAP);
 
-	if (dma_obj->map_noncoherent) {
+	if (dma_obj->cached) {
 		vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
 
 		ret = dma_mmap_pages(dma_obj->base.dev->dev,
diff --git a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
index 5ec75e9ba499..a3df2f99a757 100644
--- a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
+++ b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
@@ -919,7 +919,10 @@ ingenic_drm_gem_create_object(struct drm_device *drm, size_t size)
 	if (!obj)
 		return ERR_PTR(-ENOMEM);
 
-	obj->map_noncoherent = priv->soc_info->map_noncoherent;
+	if (priv->soc_info->map_noncoherent) {
+		obj->cached = true;
+		obj->coherent = false;
+	}
 
 	return &obj->base;
 }
diff --git a/drivers/gpu/drm/rcar-du/Kconfig b/drivers/gpu/drm/rcar-du/Kconfig
index 53c356aed5d5..dddc70c08bdc 100644
--- a/drivers/gpu/drm/rcar-du/Kconfig
+++ b/drivers/gpu/drm/rcar-du/Kconfig
@@ -2,8 +2,6 @@
 config DRM_RCAR_DU
 	tristate "DRM Support for R-Car Display Unit"
 	depends on DRM && OF
-	depends on ARM || ARM64
-	depends on ARCH_RENESAS || COMPILE_TEST
 	select DRM_KMS_HELPER
 	select DRM_GEM_DMA_HELPER
 	select VIDEOMODE_HELPERS
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_kms.c b/drivers/gpu/drm/rcar-du/rcar_du_kms.c
index adfb36b0e815..1142d51473e6 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_kms.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_kms.c
@@ -386,7 +386,9 @@ struct drm_gem_object *rcar_du_gem_prime_import_sg_table(struct drm_device *dev,
 	gem_obj->funcs = &rcar_du_gem_funcs;
 
 	drm_gem_private_object_init(dev, gem_obj, attach->dmabuf->size);
-	dma_obj->map_noncoherent = false;
+
+	dma_obj->cached = false;
+	dma_obj->coherent = false;
 
 	ret = drm_gem_create_mmap_offset(gem_obj);
 	if (ret) {
diff --git a/include/drm/drm_gem_dma_helper.h b/include/drm/drm_gem_dma_helper.h
index 8a043235dad8..585ce3d4d1eb 100644
--- a/include/drm/drm_gem_dma_helper.h
+++ b/include/drm/drm_gem_dma_helper.h
@@ -16,7 +16,9 @@ struct drm_mode_create_dumb;
  *       more than one entry but they are guaranteed to have contiguous
  *       DMA addresses.
  * @vaddr: kernel virtual address of the backing memory
- * @map_noncoherent: if true, the GEM object is backed by non-coherent memory
+ * @cached: if true, the GEM object is backed by cached memory
+ * @coherent: This option only meaningful when a GEM object is cached.
+ *            If true, Sync the GEM object for DMA access is not required.
  */
 struct drm_gem_dma_object {
 	struct drm_gem_object base;
@@ -26,7 +28,8 @@ struct drm_gem_dma_object {
 	/* For objects with DMA memory allocated by GEM DMA */
 	void *vaddr;
 
-	bool map_noncoherent;
+	bool cached;
+	bool coherent;
 };
 
 #define to_drm_gem_dma_obj(gem_obj) \
-- 
2.25.1