Re: [PATCH] drm: Fix for GEM buffers with write-combine memory

[Paul Cercueil <paul@xxxxxxxxxxxxxxx>]

Hi Tomi,

Le ven., mai 28 2021 at 08:59:15 +0300, Tomi Valkeinen 
<tomi.valkeinen@xxxxxxxxxxxxxxxx> a écrit :
> On 28/05/2021 02:03, Paul Cercueil wrote:
> > The previous commit wrongly assumed that dma_mmap_wc() could be 
> > replaced
> > by pgprot_writecombine() + dma_mmap_pages(). It did work on my setup,
> > but did not work everywhere.
> >
> > Use dma_mmap_wc() when the buffer has the write-combine cache 
> > attribute,
> > and dma_mmap_pages() when it has the non-coherent cache attribute.
> >
> > Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > Reported-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> > Fixes: cf8ccbc72d61 ("drm: Add support for GEM buffers backed by 
> > non-coherent memory")
> > ---
> >   drivers/gpu/drm/drm_gem_cma_helper.c | 16 ++++++++++------
> >   1 file changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c 
> > b/drivers/gpu/drm/drm_gem_cma_helper.c
> > index 235c7a63da2b..4c3772651954 100644
> > --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> > @@ -514,13 +514,17 @@ int drm_gem_cma_mmap(struct drm_gem_object 
> > *obj, struct vm_area_struct *vma)
> >     	cma_obj = to_drm_gem_cma_obj(obj);
> >   -	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> > -	if (!cma_obj->map_noncoherent)
> > -		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> > +	if (cma_obj->map_noncoherent) {
> > +		vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> > +
> > +		ret = dma_mmap_pages(cma_obj->base.dev->dev,
> > +				     vma, vma->vm_end - vma->vm_start,
> > +				     virt_to_page(cma_obj->vaddr));
> > +	} else {
> > +		ret = dma_mmap_wc(cma_obj->base.dev->dev, vma, cma_obj->vaddr,
> > +				  cma_obj->paddr, vma->vm_end - vma->vm_start);
> >   -	ret = dma_mmap_pages(cma_obj->base.dev->dev,
> > -			     vma, vma->vm_end - vma->vm_start,
> > -			     virt_to_page(cma_obj->vaddr));
> > +	}
> >   	if (ret)
> >   		drm_gem_vm_close(vma);
> >   
>
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
>
> and
>
> Tested-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>

Thanks, I applied it now.

> Thanks!
>
> Btw, the kernel-doc for drm_gem_cma_create doesn't quite match, as it 
> says wc is always used.

Alright, I'll send a patch later for this one too.

Cheers,
-Paul