On Sat, Nov 14, 2020 at 8:24 AM Christoph Hellwig <hch@xxxxxx> wrote:
>
> On Sat, Nov 14, 2020 at 10:17:12AM -0500, Jonathan Marek wrote:
> > +void msm_gem_sync_cache(struct drm_gem_object *obj, uint32_t flags,
> > + size_t range_start, size_t range_end)
> > +{
> > + struct msm_gem_object *msm_obj = to_msm_bo(obj);
> > + struct device *dev = msm_obj->base.dev->dev;
> > +
> > + /* exit early if get_pages() hasn't been called yet */
> > + if (!msm_obj->pages)
> > + return;
> > +
> > + /* TODO: sync only the specified range */
> > +
> > + if (flags & MSM_GEM_SYNC_FOR_DEVICE) {
> > + dma_sync_sg_for_device(dev, msm_obj->sgt->sgl,
> > + msm_obj->sgt->nents, DMA_TO_DEVICE);
> > + }
> > +
> > + if (flags & MSM_GEM_SYNC_FOR_CPU) {
> > + dma_sync_sg_for_cpu(dev, msm_obj->sgt->sgl,
> > + msm_obj->sgt->nents, DMA_FROM_DEVICE);
> > + }
>
> Splitting this helper from the only caller is rather strange, epecially
> with the two unused arguments. And I think the way this is specified
> to take a range, but ignoring it is actively dangerous. User space will
> rely on it syncing everything sooner or later and then you are stuck.
> So just define a sync all primitive for now, and if you really need a
> range sync and have actually implemented it add a new ioctl for that.
We do already have a split of ioctl "layer" which enforces valid ioctl
params, etc, and gem (or other) module code which is called by the
ioctl func. So I think it is fine to keep this split here. (Also, I
think at some point there will be a uring type of ioctl alternative
which would re-use the same gem func.)
But I do agree that the range should be respected or added later..
drm_ioctl() dispatch is well prepared for extending ioctls.
And I assume there should be some validation that the range is aligned
to cache-line? Or can we flush a partial cache line?
BR,
-R
