Re: [PATCH v10 05/10] drm/ttm: Add ttm_bo_kmap_try_from_panic()

[Christian König]

On 6/18/25 11:31, Jocelyn Falempe wrote:
> 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 <jfalempe@xxxxxxxxxx>

Reviewed-by: Christian König <christian.koenig@xxxxxxx>

Preferred through drm-misc-next, but feel free to merge it through every branch you want if it makes thinks easier for you.

Regards,
Christian.

> ---
> 
> v8:
>  * Added in v8
> 
> v9:
>  * Fix comment in ttm_bo_kmap_try_from_panic(), this can *only* be called
>    from the panic handler (Christian König)
> 
>  drivers/gpu/drm/ttm/ttm_bo_util.c | 27 +++++++++++++++++++++++++++
>  include/drm/ttm/ttm_bo.h          |  1 +
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index 15cab9bda17f..6912e6dfda25 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -377,6 +377,33 @@ 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
>   *
> diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
> index cf027558b6db..8c0ce3fa077f 100644
> --- a/include/drm/ttm/ttm_bo.h
> +++ b/include/drm/ttm/ttm_bo.h
> @@ -429,6 +429,7 @@ 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);