On Tue, Jun 25, 2013 at 5:09 AM, Inki Dae [off-list ref] wrote:

quoted

that
should be the role of kernel memory management which of course needs
synchronization btw A and B. But in no case this should be done using
dma-buf. dma-buf is for sharing content btw different devices not
sharing resources.

hmm, is that true? And are you sure? Then how do you think about
reservation? the reservation also uses dma-buf with same reason as long as I
know: actually, we use reservation to use dma-buf. As you may know, a
reservation object is allocated and initialized when a buffer object is
exported to a dma buf.

no, this is why the reservation object can be passed in when you
construction the dmabuf.  The fallback is for dmabuf to create it's
own, for compatibility and to make life easier for simple devices with
few buffers... but I think pretty much all drm drivers would embed the
reservation object in the gem buffer and pass it in when the dmabuf is
created.

It is pretty much imperative that synchronization works independently
of dmabuf, you really don't want to have two different cases to deal
with in your driver, one for synchronizing non-exported objects, and
one for synchronizing dmabuf objects.

BR,
-R