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

[Jocelyn Falempe <jfalempe@redhat.com>]

On 24/10/2025 13:53, Tvrtko Ursulin wrote:
> 
> 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?

I think it's mutter/gnome-shell who copy the buffer from i915 to ast, 
here is the logs:

gnome-shell[2079]: Failed to initialize accelerated iGPU/dGPU 
framebuffer sharing: Do not want to use software renderer (llvmpipe 
(LLVM 19.1.7, 256 bits)), falling back to CPU copy path
gnome-shell[1533]: Created gbm renderer for '/dev/dri/card0'
gnome-shell[1533]: GPU /dev/dri/card1 selected as primary

card0 is ast and card1 is i915

Do you think there is something missing in mutter?

(Added Michel Dänzer that may know more about mutter).

-- 

Jocelyn


> 
> Wondering if some path is not calling dma_buf_begin/end_cpu_access().
> 
> 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
>