Re: [PATCH 3/3] drm/cma-helper: Pass GEM CMA object in public interfaces

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Hi Laurent

Am 15.11.21 um 14:50 schrieb Laurent Pinchart:
Hi Thomas,

Thank you for the patch.

On Mon, Nov 15, 2021 at 01:01:48PM +0100, Thomas Zimmermann wrote:
Change all GEM CMA object functions that receive a GEM object
of type struct drm_gem_object to expect an object of type
struct drm_gem_cma_object instead.

This change reduces the number of upcasts from struct drm_gem_object
by moving them into callers. The C compiler can now verify that the
GEM CMA functions are called with the correct type.

For consistency, the patch also renames drm_gem_cma_free_object to
drm_gem_cma_free. It further updates documentation for a number of
functions.

I'm not convinced to be honest. I won't block this series, but I don't
really see what it brings us.

Type checking. It's much harder to accidentaly pass a wrong GEM object (SHMEM, VRAM, etc) to the functions now. I know that it's not been a super-huge problem so far, but still worth addressing IMHO.

Best regards
Thomas


Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
---
  drivers/gpu/drm/drm_gem_cma_helper.c | 52 +++++++++++++---------------
  drivers/gpu/drm/vc4/vc4_bo.c         |  4 +--
  include/drm/drm_gem_cma_helper.h     | 39 ++++++++++++---------
  3 files changed, 48 insertions(+), 47 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
index 27ccb71e3d66..7d4895de9e0d 100644
--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -32,6 +32,10 @@
   * The DRM GEM/CMA helpers use this allocator as a means to provide buffer
   * objects that are physically contiguous in memory. This is useful for
   * display drivers that are unable to map scattered buffers via an IOMMU.
+ *
+ * For GEM callback helpers in struct &drm_gem_object functions, see likewise
+ * named functions with an _object_ infix (e.g., drm_gem_cma_object_vmap() wraps
+ * drm_gem_cma_vmap()). These helpers perform the necessary type conversion.
   */
static const struct drm_gem_object_funcs drm_gem_cma_default_funcs = {
@@ -192,16 +196,16 @@ drm_gem_cma_create_with_handle(struct drm_file *file_priv,
  }
/**
- * drm_gem_cma_free_object - free resources associated with a CMA GEM object
- * @gem_obj: GEM object to free
+ * drm_gem_cma_free - free resources associated with a CMA GEM object
+ * @cma_obj: CMA GEM object to free
   *
   * This function frees the backing memory of the CMA GEM object, cleans up the
   * GEM object state and frees the memory used to store the object itself.
   * If the buffer is imported and the virtual address is set, it is released.
   */
-void drm_gem_cma_free_object(struct drm_gem_object *gem_obj)
+void drm_gem_cma_free(struct drm_gem_cma_object *cma_obj)
  {
-	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(gem_obj);
+	struct drm_gem_object *gem_obj = &cma_obj->base;
  	struct dma_buf_map map = DMA_BUF_MAP_INIT_VADDR(cma_obj->vaddr);
if (gem_obj->import_attach) {
@@ -222,7 +226,7 @@ void drm_gem_cma_free_object(struct drm_gem_object *gem_obj)
kfree(cma_obj);
  }
-EXPORT_SYMBOL_GPL(drm_gem_cma_free_object);
+EXPORT_SYMBOL_GPL(drm_gem_cma_free);
/**
   * drm_gem_cma_dumb_create_internal - create a dumb buffer object
@@ -369,18 +373,15 @@ EXPORT_SYMBOL_GPL(drm_gem_cma_get_unmapped_area);
/**
   * drm_gem_cma_print_info() - Print &drm_gem_cma_object info for debugfs
+ * @cma_obj: CMA GEM object
   * @p: DRM printer
   * @indent: Tab indentation level
- * @obj: GEM object
   *
- * This function can be used as the &drm_driver->gem_print_info callback.
- * It prints paddr and vaddr for use in e.g. debugfs output.
+ * This function prints paddr and vaddr for use in e.g. debugfs output.
   */
-void drm_gem_cma_print_info(struct drm_printer *p, unsigned int indent,
-			    const struct drm_gem_object *obj)
+void drm_gem_cma_print_info(const struct drm_gem_cma_object *cma_obj,
+			    struct drm_printer *p, unsigned int indent)
  {
-	const struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
-
  	drm_printf_indent(p, indent, "paddr=%pad\n", &cma_obj->paddr);
  	drm_printf_indent(p, indent, "vaddr=%p\n", cma_obj->vaddr);
  }
@@ -389,7 +390,7 @@ EXPORT_SYMBOL(drm_gem_cma_print_info);
  /**
   * drm_gem_cma_get_sg_table - provide a scatter/gather table of pinned
   *     pages for a CMA GEM object
- * @obj: GEM object
+ * @cma_obj: CMA GEM object
   *
   * This function exports a scatter/gather table by calling the standard
   * DMA mapping API.
@@ -397,9 +398,9 @@ EXPORT_SYMBOL(drm_gem_cma_print_info);
   * Returns:
   * A pointer to the scatter/gather table of pinned pages or NULL on failure.
   */
-struct sg_table *drm_gem_cma_get_sg_table(struct drm_gem_object *obj)
+struct sg_table *drm_gem_cma_get_sg_table(struct drm_gem_cma_object *cma_obj)
  {
-	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
+	struct drm_gem_object *obj = &cma_obj->base;
  	struct sg_table *sgt;
  	int ret;
@@ -465,22 +466,19 @@ EXPORT_SYMBOL_GPL(drm_gem_cma_prime_import_sg_table);
  /**
   * drm_gem_cma_vmap - map a CMA GEM object into the kernel's virtual
   *     address space
- * @obj: GEM object
+ * @cma_obj: CMA GEM object
   * @map: Returns the kernel virtual address of the CMA GEM object's backing
   *       store.
   *
- * This function maps a buffer into the kernel's
- * virtual address space. Since the CMA buffers are already mapped into the
- * kernel virtual address space this simply returns the cached virtual
- * address.
+ * This function maps a buffer into the kernel's virtual address space.
+ * Since the CMA buffers are already mapped into the kernel virtual address
+ * space this simply returns the cached virtual address.
   *
   * Returns:
   * 0 on success, or a negative error code otherwise.
   */
-int drm_gem_cma_vmap(struct drm_gem_object *obj, struct dma_buf_map *map)
+int drm_gem_cma_vmap(struct drm_gem_cma_object *cma_obj, struct dma_buf_map *map)
  {
-	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
-
  	dma_buf_map_set_vaddr(map, cma_obj->vaddr);
return 0;
@@ -489,7 +487,7 @@ EXPORT_SYMBOL_GPL(drm_gem_cma_vmap);
/**
   * drm_gem_cma_mmap - memory-map an exported CMA GEM object
- * @obj: GEM object
+ * @cma_obj: CMA GEM object
   * @vma: VMA for the area to be mapped
   *
   * This function maps a buffer into a userspace process's address space.
@@ -499,9 +497,9 @@ EXPORT_SYMBOL_GPL(drm_gem_cma_vmap);
   * Returns:
   * 0 on success or a negative error code on failure.
   */
-int drm_gem_cma_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
+int drm_gem_cma_mmap(struct drm_gem_cma_object *cma_obj, struct vm_area_struct *vma)
  {
-	struct drm_gem_cma_object *cma_obj;
+	struct drm_gem_object *obj = &cma_obj->base;
  	int ret;
/*
@@ -512,8 +510,6 @@ int drm_gem_cma_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
  	vma->vm_pgoff -= drm_vma_node_start(&obj->vma_node);
  	vma->vm_flags &= ~VM_PFNMAP;
- cma_obj = to_drm_gem_cma_obj(obj);
-
  	if (cma_obj->map_noncoherent) {
  		vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo.c
index 830756b3159e..6d1281a343e9 100644
--- a/drivers/gpu/drm/vc4/vc4_bo.c
+++ b/drivers/gpu/drm/vc4/vc4_bo.c
@@ -177,7 +177,7 @@ static void vc4_bo_destroy(struct vc4_bo *bo)
  		bo->validated_shader = NULL;
  	}
- drm_gem_cma_free_object(obj);
+	drm_gem_cma_free(&bo->base);
  }
static void vc4_bo_remove_from_cache(struct vc4_bo *bo)
@@ -720,7 +720,7 @@ static int vc4_gem_object_mmap(struct drm_gem_object *obj, struct vm_area_struct
  		return -EINVAL;
  	}
- return drm_gem_cma_mmap(obj, vma);
+	return drm_gem_cma_mmap(&bo->base, vma);
  }
static const struct vm_operations_struct vc4_vm_ops = {
diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h
index 56d2f9fdf9ac..adb507a9dbf0 100644
--- a/include/drm/drm_gem_cma_helper.h
+++ b/include/drm/drm_gem_cma_helper.h
@@ -32,28 +32,23 @@ struct drm_gem_cma_object {
  #define to_drm_gem_cma_obj(gem_obj) \
  	container_of(gem_obj, struct drm_gem_cma_object, base)
-/* free GEM object */
-void drm_gem_cma_free_object(struct drm_gem_object *gem_obj);
-
-/* allocate physical memory */
  struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm,
  					      size_t size);
+void drm_gem_cma_free(struct drm_gem_cma_object *cma_obj);
+void drm_gem_cma_print_info(const struct drm_gem_cma_object *cma_obj,
+			    struct drm_printer *p, unsigned int indent);
+struct sg_table *drm_gem_cma_get_sg_table(struct drm_gem_cma_object *cma_obj);
+int drm_gem_cma_vmap(struct drm_gem_cma_object *cma_obj, struct dma_buf_map *map);
+int drm_gem_cma_mmap(struct drm_gem_cma_object *cma_obj, struct vm_area_struct *vma);
extern const struct vm_operations_struct drm_gem_cma_vm_ops; -void drm_gem_cma_print_info(struct drm_printer *p, unsigned int indent,
-			    const struct drm_gem_object *obj);
-
-struct sg_table *drm_gem_cma_get_sg_table(struct drm_gem_object *obj);
-int drm_gem_cma_vmap(struct drm_gem_object *obj, struct dma_buf_map *map);
-int drm_gem_cma_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma);
-
  /*
   * GEM object functions
   */
/**
- * drm_gem_cma_object_free - GEM object function for drm_gem_cma_free_object()
+ * drm_gem_cma_object_free - GEM object function for drm_gem_cma_free()
   * @obj: GEM object to free
   *
   * This function wraps drm_gem_cma_free_object(). Drivers that employ the CMA helpers
@@ -61,7 +56,9 @@ int drm_gem_cma_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma);
   */
  static inline void drm_gem_cma_object_free(struct drm_gem_object *obj)
  {
-	drm_gem_cma_free_object(obj);
+	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
+
+	drm_gem_cma_free(cma_obj);
  }
/**
@@ -76,7 +73,9 @@ static inline void drm_gem_cma_object_free(struct drm_gem_object *obj)
  static inline void drm_gem_cma_object_print_info(struct drm_printer *p, unsigned int indent,
  						 const struct drm_gem_object *obj)
  {
-	drm_gem_cma_print_info(p, indent, obj);
+	const struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
+
+	drm_gem_cma_print_info(cma_obj, p, indent);
  }
/**
@@ -91,7 +90,9 @@ static inline void drm_gem_cma_object_print_info(struct drm_printer *p, unsigned
   */
  static inline struct sg_table *drm_gem_cma_object_get_sg_table(struct drm_gem_object *obj)
  {
-	return drm_gem_cma_get_sg_table(obj);
+	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
+
+	return drm_gem_cma_get_sg_table(cma_obj);
  }
/*
@@ -107,7 +108,9 @@ static inline struct sg_table *drm_gem_cma_object_get_sg_table(struct drm_gem_ob
   */
  static inline int drm_gem_cma_object_vmap(struct drm_gem_object *obj, struct dma_buf_map *map)
  {
-	return drm_gem_cma_vmap(obj, map);
+	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
+
+	return drm_gem_cma_vmap(cma_obj, map);
  }
/**
@@ -123,7 +126,9 @@ static inline int drm_gem_cma_object_vmap(struct drm_gem_object *obj, struct dma
   */
  static inline int drm_gem_cma_object_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
  {
-	return drm_gem_cma_mmap(obj, vma);
+	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
+
+	return drm_gem_cma_mmap(cma_obj, vma);
  }
/*


--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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