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

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Hey,

On 2025-06-18 15:55, Christian König wrote:
> 
> 
> 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@redhat.com>
> 
> Reviewed-by: Christian König <christian.koenig@amd.com>
> 
> Preferred through drm-misc-next, but feel free to merge it through every branch you want if it makes thinks easier for you.
> 
Thanks for the ack there. I had to merge this patch through drm-intel-next-queued because of a rework affecting the series.

Kind regards,
~Maarten
> 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);
>