On Tue, Jan 30, 2024 at 12:10:31PM +0100, Daniel Vetter wrote:
> On Mon, Jan 29, 2024 at 06:31:19PM +0800, Julia Zhang wrote:
> > As vram objects don't have backing pages and thus can't implement
> > drm_gem_object_funcs.get_sg_table callback. This removes drm dma-buf
> > callbacks in virtgpu_gem_map_dma_buf()/virtgpu_gem_unmap_dma_buf()
> > and implement virtgpu specific map/unmap/attach callbacks to support
> > both of shmem objects and vram objects.
> >
> > Signed-off-by: Julia Zhang <julia.zhang@xxxxxxx>
> > ---
> > drivers/gpu/drm/virtio/virtgpu_prime.c | 40 +++++++++++++++++++++++---
> > 1 file changed, 36 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/virtio/virtgpu_prime.c b/drivers/gpu/drm/virtio/virtgpu_prime.c
> > index 44425f20d91a..b490a5343b06 100644
> > --- a/drivers/gpu/drm/virtio/virtgpu_prime.c
> > +++ b/drivers/gpu/drm/virtio/virtgpu_prime.c
> > @@ -49,11 +49,26 @@ virtgpu_gem_map_dma_buf(struct dma_buf_attachment *attach,
> > {
> > struct drm_gem_object *obj = attach->dmabuf->priv;
> > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
> > + struct sg_table *sgt;
> > + int ret;
> >
> > if (virtio_gpu_is_vram(bo))
> > return virtio_gpu_vram_map_dma_buf(bo, attach->dev, dir);
> >
> > - return drm_gem_map_dma_buf(attach, dir);
> > + sgt = drm_prime_pages_to_sg(obj->dev,
> > + to_drm_gem_shmem_obj(obj)->pages,
> > + obj->size >> PAGE_SHIFT);
> > + if (IS_ERR(sgt))
> > + return sgt;
> > +
> > + ret = dma_map_sgtable(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC);
> > + if (ret) {
> > + sg_free_table(sgt);
> > + kfree(sgt);
> > + return ERR_PTR(ret);
> > + }
> > +
> > + return sgt;
> > }
> >
> > static void virtgpu_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
> > @@ -63,12 +78,29 @@ static void virtgpu_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
> > struct drm_gem_object *obj = attach->dmabuf->priv;
> > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
> >
> > + if (!sgt)
> > + return;
> > +
> > if (virtio_gpu_is_vram(bo)) {
> > virtio_gpu_vram_unmap_dma_buf(attach->dev, sgt, dir);
> > - return;
> > + } else {
> > + dma_unmap_sgtable(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC);
> > + sg_free_table(sgt);
> > + kfree(sgt);
> > }
> > +}
> > +
> > +static int virtgpu_gem_device_attach(struct dma_buf *dma_buf,
> > + struct dma_buf_attachment *attach)
> > +{
> > + struct drm_gem_object *obj = attach->dmabuf->priv;
> > + struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
> > + int ret = 0;
> > +
> > + if (!virtio_gpu_is_vram(bo) && obj->funcs->pin)
> > + ret = obj->funcs->pin(obj);
> >
> > - drm_gem_unmap_dma_buf(attach, sgt, dir);
> > + return ret;
>
> This doesn't look like what I've expected. There should be no need to
> change the map/unmap functions, especially not for the usual gem bo case.
> We should definitely keep using the exact same code for that. Instead all
> I expected is roughly
>
> virtgpu_gem_device_attach()
> {
> if (virtio_gpu_is_vram(bo)) {
> if (can_access_virtio_vram_directly(attach->dev)
> return 0;
> else
> return -EBUSY;
> } else {
> return drm_gem_map_attach();
> }
> }
>
> Note that I think can_access_virtio_vram_directly() needs to be
> implemented first. I'm not even sure it's possible, might be that all the
> importers need to set the attachment->peer2peer flag. Which is why this
> thing exists really. But that's a pile more work to do.
>
> Frankly the more I look at the original patch that added vram export
> support the more this just looks like a "pls revert, this is just too
> broken".
The commit I mean is this one: ea5ea3d8a117 ("drm/virtio: support mapping
exported vram"). The commit message definitely needs to cite that one, and
also needs a cc: stable because not rejecting invalid imports is a pretty
big deal.
Also adding David.
-Sima
>
> We should definitely not open-code any functions for the gem_bo export
> case, which your patch seems to do? Or maybe I'm just extremely confused.
> -Sima
>
> >
> > static const struct virtio_dma_buf_ops virtgpu_dmabuf_ops = {
> > @@ -83,7 +115,7 @@ static const struct virtio_dma_buf_ops virtgpu_dmabuf_ops = {
> > .vmap = drm_gem_dmabuf_vmap,
> > .vunmap = drm_gem_dmabuf_vunmap,
> > },
> > - .device_attach = drm_gem_map_attach,
> > + .device_attach = virtgpu_gem_device_attach,
> > .get_uuid = virtgpu_virtio_get_uuid,
> > };
> >
> > --
> > 2.34.1
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
