Quoting Laurent Pinchart (2017-08-18 09:01:38) > Hi Daniel, > > On Friday 18 Aug 2017 09:45:48 Daniel Vetter wrote: > > On Fri, Aug 18, 2017 at 01:35:41AM +0300, Laurent Pinchart wrote: > > > Fair enough. I wonder, however, why mmap()ing an imported buffer through > > > the dumb buffers API is an invalid use case, while doing the same through > > > the driver-specific buffer API isn't. > > > > Because i915 is special. Our offset-based mmap goes throug the gart, and > > for that all we need is to dma-map the sg table, which is the primary > > use-case for dma-buf. Which means we can always do that. But yeah it's > > special. > > I'll take this as meaning that i915 shouldn't allow this use case, but does > and will need to continue doing so because we can't break userspace (it would > be nice to start moving userspace away from mmap()ing imported buffers > though).
We do like pretend ingthat all GEM handles userspace has are equal. Partly this is due to the lack of side-channels in protocols like DRI2/DRI3 where all shared buffers must be fully capable or else either party may die in weird ways. Keeping everything first class allows for a simple agnostic userspace. Alas that is not the case, but the one thing we do have atm is that we can rely on using a mmap via the GTT. If we throw that out the window, we have teach all of our userspace about transfer buffers as the final fallback. (Yes, history repeats.) -Chris _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
