Re: [PATCH 3/5] drm: Add and export function drm_gem_cma_mmap_noncoherent

[Paul Cercueil]

Hi Christoph,

Le mar. 3 nov. 2020 à 19:13, Paul Cercueil <paul@xxxxxxxxxxxxxxx> a 
écrit :
> Hi Christoph,
>
> Le mar. 3 nov. 2020 à 18:50, Christoph Hellwig <hch@xxxxxxxxxxxxx> a 
> écrit :
> > On Mon, Nov 02, 2020 at 10:06:49PM +0000, Paul Cercueil wrote:
> > >  This function can be used by drivers that need to mmap dumb buffers
> > >  created with non-coherent backing memory.
> > >
> > >  Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > >  ---
> > >   drivers/gpu/drm/drm_gem_cma_helper.c | 39 
> > > ++++++++++++++++++++++++++++
> > >   include/drm/drm_gem_cma_helper.h     |  2 ++
> > >   2 files changed, 41 insertions(+)
> > >
> > >  diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c 
> > > b/drivers/gpu/drm/drm_gem_cma_helper.c
> > >  index 3bdd67795e20..4ed63f4896bd 100644
> > >  --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> > >  +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> > >  @@ -387,6 +387,45 @@ int drm_gem_cma_mmap(struct file *filp, 
> > > struct vm_area_struct *vma)
> > >   }
> > >   EXPORT_SYMBOL_GPL(drm_gem_cma_mmap);
> > >
> > >  +/**
> > >  + * drm_gem_cma_mmap_noncoherent - memory-map a CMA GEM object with
> > >  + *     non-coherent cache attribute
> > >  + * @filp: file object
> > >  + * @vma: VMA for the area to be mapped
> > >  + *
> > >  + * Just like drm_gem_cma_mmap, but for a GEM object backed by 
> > > non-coherent
> > >  + * memory.
> > >  + *
> > >  + * Returns:
> > >  + * 0 on success or a negative error code on failure.
> > >  + */
> > >  +int drm_gem_cma_mmap_noncoherent(struct file *filp, struct 
> > > vm_area_struct *vma)
> > >  +{
> > >  +	struct drm_gem_cma_object *cma_obj;
> > >  +	int ret;
> > >  +
> > >  +	ret = drm_gem_mmap(filp, vma);
> > >  +	if (ret)
> > >  +		return ret;
> > >  +
> > >  +	cma_obj = to_drm_gem_cma_obj(vma->vm_private_data);
> > >  +
> > >  +	/*
> > >  +	 * Clear the VM_PFNMAP flag that was set by drm_gem_mmap(), and 
> > > set the
> > >  +	 * vm_pgoff (used as a fake buffer offset by DRM) to 0 as we 
> > > want to map
> > >  +	 * the whole buffer.
> > >  +	 */
> > >  +	vma->vm_flags &= ~VM_PFNMAP;
> > >  +	vma->vm_pgoff = 0;
> > >  +	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> > >  +
> > >  +	return remap_pfn_range(vma, vma->vm_start,
> > >  +			       cma_obj->paddr >> PAGE_SHIFT,
> > >  +			       vma->vm_end - vma->vm_start,
> > >  +			       vma->vm_page_prot);
> >
> > Per patch 1 cma_obj->paddr is the dma address, while remap_pfn_range
> > expects a physical address.  This does not work.
>
> Ok, what would be the correct way to mmap_noncoherent?

Waiting for your input here :)

Cheers,
-Paul