drm/gpuvm: Helper to get range of unmap from a remap op.

Determining the start and range of the unmap stage of a remap op is a
common piece of code currently implemented by multiple drivers. Add a
helper for this.

Changes since v7:
- Renamed helper to drm_gpuva_op_remap_to_unmap_range()
- Improved documentation

Changes since v6:
- Remove use of __always_inline
Signed-off-by: Donald Robson <donald.robson@imgtec.com>
Signed-off-by: Sarah Walker <sarah.walker@imgtec.com>
Reviewed-by: Danilo Krummrich <dakr@redhat.com>
Link: https://lore.kernel.org/r/8a0a5b5eeec459d3c60fcdaa5a638ad14a18a59e.1700668843.git.donald.robson@imgtec.comSigned-off-by: Maxime Ripard <mripard@kernel.org>

include/drm/drm_gpuvm.h

@@ -1213,4 +1213,32 @@ void drm_gpuva_remap(struct drm_gpuva *prev,
 
 void drm_gpuva_unmap(struct drm_gpuva_op_unmap *op);
 
+/**
+ * drm_gpuva_op_remap_to_unmap_range() - Helper to get the start and range of
+ * the unmap stage of a remap op.
+ * @op: Remap op.
+ * @start_addr: Output pointer for the start of the required unmap.
+ * @range: Output pointer for the length of the required unmap.
+ *
+ * The given start address and range will be set such that they represent the
+ * range of the address space that was previously covered by the mapping being
+ * re-mapped, but is now empty.
+ */
+static inline void
+drm_gpuva_op_remap_to_unmap_range(const struct drm_gpuva_op_remap *op,
+				  u64 *start_addr, u64 *range)
+{
+	const u64 va_start = op->prev ?
+			     op->prev->va.addr + op->prev->va.range :
+			     op->unmap->va->va.addr;
+	const u64 va_end = op->next ?
+			   op->next->va.addr :
+			   op->unmap->va->va.addr + op->unmap->va->va.range;
+
+	if (start_addr)
+		*start_addr = va_start;
+	if (range)
+		*range = va_end - va_start;
+}
+
 #endif /* __DRM_GPUVM_H__ */