Re: [RFC] dma-buf: Implement test module

[Thomas Hellstrom]

On 12/14/2013 02:02 PM, Rob Clark wrote:
> On Sat, Dec 14, 2013 at 7:47 AM, Thomas Hellstrom <thomas@xxxxxxxxxxxx> wrote:
> > On 12/14/2013 01:37 PM, Thierry Reding wrote:
> > > On Thu, Dec 12, 2013 at 11:30:23PM +0100, Daniel Vetter wrote:
> > > > On Thu, Dec 12, 2013 at 8:34 PM, Thomas Hellstrom <thellstrom@xxxxxxxxxx>
> > > > wrote:
> > > > > On 12/12/2013 03:36 PM, Thierry Reding wrote:
> > > > > > This is a simple test module that can be used to allocate, export and
> > > > > > delete DMA-BUF objects. It can be used to test DMA-BUF sharing in
> > > > > > systems that lack a real second driver.
> > > > > Looks nice. I wonder whether this could be extended to create a
> > > > > "streaming"
> > > > > dma-buf from a user space mapping. That could be used as a generic way
> > > > > to
> > > > > implement streaming (user) buffer objects, rather than to add explicit
> > > > > support for those in, for example, TTM.
> > > > Atm there's no way to get gpus to unbind their dma-buf mappings, so
> > > > their essentially pinned forever from first use on.
> > > Shouldn't this work by simply calling the GEM_CLOSE IOCTL on the handle
> > > returned by drmPrimeFDToHandle()? I mean that should drop the last
> > > reference on the GEM object and cause it to be cleaned up (which should
> > > include detaching the DMA-BUF).
> >
> > Actually, while the GEM prime implementation appears to pin an exported
> > dma-buf on first attach, from the dma-buf documentation it seems sufficient
> > to pin it on map or cpu access.
> >
> > But what I assume Daniel is referring to is that there is no way for
> > exporters to tell importers to force unmap() the dma-buf, so that it can be
> > unpinned?
> yeah, or some way for importers to opportunistically keep around a
> mapping rather than map/unmap on each use..
>
> maybe we need something shrinker-ish for dmabuf?

Yes, I think that's needed for both the memory-shortage case where we 
want to unpin, and I guess it would desirable for
iommu space management as well.

/Thomas

> BR,
> -R
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