drm/ttm: Add ttm_bo_kmap_try_from_panic()

If the ttm bo is backed by pages, then it's possible to safely kmap
one page at a time, using kmap_try_from_panic().
Unfortunately there is no way to do the same with ioremap, so it
only supports the kmap case.
This is needed for proper drm_panic support with xe driver.

Signed-off-by: Jocelyn Falempe <[email protected]>
Reviewed-by: Christian König <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Maarten Lankhorst <[email protected]>

Author: Jocelyn Falempe

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -381,6 +381,33 @@ static int ttm_bo_kmap_ttm(struct ttm_buffer_object *bo,
 	return (!map->virtual) ? -ENOMEM : 0;
 }
 
+/**
+ *
+ * ttm_bo_kmap_try_from_panic
+ *
+ * @bo: The buffer object
+ * @page: The page to map
+ *
+ * Sets up a kernel virtual mapping using kmap_local_page_try_from_panic().
+ * This should only be called from the panic handler, if you make sure the bo
+ * is the one being displayed, so is properly allocated, and protected.
+ *
+ * Returns the vaddr, that you can use to write to the bo, and that you should
+ * pass to kunmap_local() when you're done with this page, or NULL if the bo
+ * is in iomem.
+ */
+void *ttm_bo_kmap_try_from_panic(struct ttm_buffer_object *bo, unsigned long page)
+{
+	if (page + 1 > PFN_UP(bo->resource->size))
+		return NULL;
+
+	if (!bo->resource->bus.is_iomem && bo->ttm->pages && bo->ttm->pages[page])
+		return kmap_local_page_try_from_panic(bo->ttm->pages[page]);
+
+	return NULL;
+}
+EXPORT_SYMBOL(ttm_bo_kmap_try_from_panic);
+
 /**
  * ttm_bo_kmap
  *

include/drm/ttm/ttm_bo.h

@@ -401,6 +401,7 @@ int ttm_bo_init_validate(struct ttm_device *bdev, struct ttm_buffer_object *bo,
 int ttm_bo_kmap(struct ttm_buffer_object *bo, unsigned long start_page,
 		unsigned long num_pages, struct ttm_bo_kmap_obj *map);
 void ttm_bo_kunmap(struct ttm_bo_kmap_obj *map);
+void *ttm_bo_kmap_try_from_panic(struct ttm_buffer_object *bo, unsigned long page);
 int ttm_bo_vmap(struct ttm_buffer_object *bo, struct iosys_map *map);
 void ttm_bo_vunmap(struct ttm_buffer_object *bo, struct iosys_map *map);
 int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo);