Re: [PATCH] drm/i915/dmabuf: Flush the cache in vmap

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 24.10.25 um 13:53 schrieb Tvrtko Ursulin:
>
> On 24/10/2025 12:04, Jocelyn Falempe wrote:
>> On a lenovo se100 server, when using i915 GPU for rendering, and the
>> ast driver for display, the graphic output is corrupted, and almost
>> unusable.
>>
>> Adding a clflush call in the vmap function fixes this issue
>> completely.
>
> AST is importing i915 allocated buffer in this use case, or how 
> exactly is the relationship?
>
> Wondering if some path is not calling dma_buf_begin/end_cpu_access().

Yes, ast doesn't call begin/end_cpu_access in [1].

Jocelyn, if that fixes the issue, feel free to send me a patch for review.

[1] 
https://elixir.bootlin.com/linux/v6.17.4/source/drivers/gpu/drm/ast/ast_mode.c

Best regards
Thomas

>
> Regards,
>
> Tvrtko
>
>>
>> Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
>> ---
>>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c 
>> b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> index f4f1c979d1b9..f6a8c1cbe4d1 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> @@ -77,6 +77,7 @@ static int i915_gem_dmabuf_vmap(struct dma_buf 
>> *dma_buf,
>>           return PTR_ERR(vaddr);
>>         iosys_map_set_vaddr(map, vaddr);
>> +    drm_clflush_virt_range(vaddr, dma_buf->size);
>>         return 0;
>>   }
>>
>> base-commit: 0790925dadad0997580df6e32cdccd54316807f2
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)