[Intel-gfx] [PATCH 7/9] drm/shmem-helpers: Redirect mmap for imported dma-buf

[Daniel Vetter]

On Thu, May 14, 2020 at 09:23:37AM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 11.05.20 um 11:35 schrieb Daniel Vetter:
> > Currently this seems to work by converting the sgt into a pages array,
> > and then treating it like a native object. Do the right thing and
> > redirect mmap to the exporter.
> > 
> > With this nothing is calling get_pages anymore on imported dma-buf,
> > and we can start to remove the use of the ->pages array for that case.
> > 
> > v2: Rebase
> > 
> > Cc: Gerd Hoffmann <kraxel at redhat.com>
> > Cc: Rob Herring <robh at kernel.org>
> > Cc: Noralf Trønnes <noralf at tronnes.org>
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > ---
> >  drivers/gpu/drm/drm_gem_shmem_helper.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > index b9cba5cc61c3..117a7841e284 100644
> > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > @@ -551,6 +551,9 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
> >  	/* Remove the fake offset */
> >  	vma->vm_pgoff -= drm_vma_node_start(&obj->vma_node);
> >  
> > +	if (obj->import_attach)
> > +		return dma_buf_mmap(obj->dma_buf, vma, 0);
> > +
> 
> Just a question: how does it work with the fake value in vm_pgoffset?
> The offset is a DRM-specific thing and the dma-buf exporter expects the
> real offset?

For drm chardev file descriptor we have one file, but want to let
userspace map arbitrary objects. So an object gets a allocated an area
within the over drm mmap space, this fake offset.

For dma-buf mmap otoh there's a 1:1 mapping between fd and object, so no
additional offset needed.
-Daniel

> 
> With this question clarified:
> 
> Acked-by: Thomas Zimmermann <tzimmermann at suse.de>
> 
> 
> >  	shmem = to_drm_gem_shmem_obj(obj);
> >  
> >  	ret = drm_gem_shmem_get_pages(shmem);
> > 
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
> 




-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch