On Wed, Apr 17, 2019 at 04:30:51PM +0200, Daniel Vetter wrote: > On Wed, Apr 17, 2019 at 04:20:02PM +0200, Daniel Vetter wrote: > > On Tue, Apr 16, 2019 at 08:38:34PM +0200, Christian König wrote: > > > Add optional explicit pinning callbacks instead of implicitly assume the > > > exporter pins the buffer when a mapping is created. > > > > > > Signed-off-by: Christian König <christian.koenig@xxxxxxx> > > > > Don't we need this together with the invalidate callback and the dynamic > > stuff? Also I'm assuming that pin/unpin is pretty much required for > > dynamic bo, so could we look at these callbacks instead of the dynamic > > flag you add in patch 1. > > > > I'm assuming following rules hold: > > no pin/upin from exporter: > > > > dma-buf is not dynamic, and pinned for the duration of map/unmap. I'm > > not 100% sure whether really everyone wants the mapping to be cached for > > the entire attachment, only drm_prime does that. And that's not the only > > dma-buf importer. > > > > pin/unpin calls are noops. > > > > pin/unpin exist in the exporter, but importer has not provided an > > invalidate callback: > > > > We map at attach time, and we also have to pin, since the importer can't > > handle the buffer disappearing, at attach time. We unmap/unpin at detach. > > For this case we should have a WARN in pin/unpin, to make sure importers > don't do something stupid. One more thought below on pin/unpin. > > > pin/unpin from exporter, invalidate from importer: > > > > Full dynamic mapping. We assume the importer will do caching, attach > > fences as needed, and pin the underlying bo when it needs it it > > permanently, without attaching fences (i.e. the scanout case). > > > > Assuming I'm not terribly off with my understanding, then I think it'd be > > best to introduce the entire new dma-buf api in the first patch, and flesh > > it out later. Instead of spread over a few patches. Plus the above (maybe > > prettier) as a nice kerneldoc overview comment for how dynamic dma-buf is > > supposed to work really. > > -Daniel > > > > > --- > > > drivers/dma-buf/dma-buf.c | 39 +++++++++++++++++++++++++++++++++++++++ > > > include/linux/dma-buf.h | 37 +++++++++++++++++++++++++++++++------ > > > 2 files changed, 70 insertions(+), 6 deletions(-) > > > > > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > > > index a3738fab3927..f23ff8355505 100644 > > > --- a/drivers/dma-buf/dma-buf.c > > > +++ b/drivers/dma-buf/dma-buf.c > > > @@ -630,6 +630,41 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) > > > } > > > EXPORT_SYMBOL_GPL(dma_buf_detach); > > > > > > +/** > > > + * dma_buf_pin - Lock down the DMA-buf > > > + * > > > + * @dmabuf: [in] DMA-buf to lock down. > > > + * > > > + * Returns: > > > + * 0 on success, negative error code on failure. > > > + */ > > > +int dma_buf_pin(struct dma_buf *dmabuf) > > Hm, I think it'd be better to pin the attachment, not the underlying > buffer. Attachment is the thin the importer will have to pin, and it's at > attach/detach time where dma-buf needs to pin for importers who don't > understand dynamic buffer sharing. > > Plus when we put that onto attachments, we can do a > > WARN_ON(!attach->invalidate); > > sanity check. I think that would be good to have. Another validation idea: dma-buf.c could track the pin_count on the struct dma_buf, and if an exporter tries to invalidate while pinned WARN and bail out. Because that's clearly a driver bug. All in the interest in making the contract between importers and exporters as clear as possible. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
