drm/ttm: Add ttm_bo_access

Non-contiguous VRAM cannot easily be mapped in TTM nor can non-visible
VRAM easily be accessed. Add ttm_bo_access, which is similar to
ttm_bo_vm_access, to access such memory.

v4:
 - Fix checkpatch warnings (CI)
v5:
 - Fix checkpatch warnings (CI)
v6:
 - Fix kernel doc (Auld)
v7:
 - Move ttm_bo_access to ttm_bo_vm.c (Christian)

Cc: Christian König <christian.koenig@amd.com>
Reported-by: Christoph Manszewski <christoph.manszewski@intel.com>
Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Tested-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241126174615.2665852-3-matthew.brost@intel.com

Author: mbrost05

drivers/gpu/drm/ttm/ttm_bo_vm.c

@@ -405,13 +405,25 @@ static int ttm_bo_vm_access_kmap(struct ttm_buffer_object *bo,
 	return len;
 }
 
-int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
-		     void *buf, int len, int write)
+/**
+ * ttm_bo_access - Helper to access a buffer object
+ *
+ * @bo: ttm buffer object
+ * @offset: access offset into buffer object
+ * @buf: pointer to caller memory to read into or write from
+ * @len: length of access
+ * @write: write access
+ *
+ * Utility function to access a buffer object. Useful when buffer object cannot
+ * be easily mapped (non-contiguous, non-visible, etc...). Should not directly
+ * be exported to user space via a peak / poke interface.
+ *
+ * Returns:
+ * @len if successful, negative error code on failure.
+ */
+int ttm_bo_access(struct ttm_buffer_object *bo, unsigned long offset,
+		  void *buf, int len, int write)
 {
-	struct ttm_buffer_object *bo = vma->vm_private_data;
-	unsigned long offset = (addr) - vma->vm_start +
-		((vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node))
-		 << PAGE_SHIFT);
 	int ret;
 
 	if (len < 1 || (offset + len) > bo->base.size)
@@ -429,8 +441,8 @@ int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
 		break;
 	default:
 		if (bo->bdev->funcs->access_memory)
-			ret = bo->bdev->funcs->access_memory(
-				bo, offset, buf, len, write);
+			ret = bo->bdev->funcs->access_memory
+				(bo, offset, buf, len, write);
 		else
 			ret = -EIO;
 	}
@@ -439,6 +451,18 @@ int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
 
 	return ret;
 }
+EXPORT_SYMBOL(ttm_bo_access);
+
+int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
+		     void *buf, int len, int write)
+{
+	struct ttm_buffer_object *bo = vma->vm_private_data;
+	unsigned long offset = (addr) - vma->vm_start +
+		((vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node))
+		 << PAGE_SHIFT);
+
+	return ttm_bo_access(bo, offset, buf, len, write);
+}
 EXPORT_SYMBOL(ttm_bo_vm_access);
 
 static const struct vm_operations_struct ttm_bo_vm_ops = {

include/drm/ttm/ttm_bo.h

@@ -421,6 +421,8 @@ void ttm_bo_unpin(struct ttm_buffer_object *bo);
 int ttm_bo_evict_first(struct ttm_device *bdev,
 		       struct ttm_resource_manager *man,
 		       struct ttm_operation_ctx *ctx);
+int ttm_bo_access(struct ttm_buffer_object *bo, unsigned long offset,
+		  void *buf, int len, int write);
 vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
 			     struct vm_fault *vmf);
 vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,