[Linaro-mm-sig] Memory Management Discussion

rmorell at nvidia.com rmorell at nvidia.com
Wed Apr 20 02:06:10 UTC 2011

On Tue, Apr 19, 2011 at 06:52:53PM -0700, Clark, Rob wrote:
> On Mon, Apr 18, 2011 at 9:45 AM, Sree Kumar <sreeon at gmail.com> wrote:
> > Thanks Jesse for initiating the mailing list.
> >
> > We need to address the requirements of Graphics and Multimedia Accelerators
> > (IPs).
> > What we really need is a permanent solution (at upstream) which accommodates
> > the following requirements and conforms to Graphics and Multimedia use
> > cases.
> >
> > 1.Mechanism to map/unmap the memory. Some of the IPs’ have the ability to
> > address virtual memory and some can address only physically contiguous
> > address space. We need to address both these cases.
> > 2.Mechanism to allocate and release memory.
> > 3.Method to share the memory (ZERO copy is a MUST for better performance)
> > between different device drivers (example output of camera to multimedia
> > encoder).
> > 4.Method to share the memory with different processes in userspace. The
> > sharing mechanism should include built-in security features.
> >
> > Are there any special requirements from V4L or DRM perspectives?
> From DRI perspective.. I guess the global buffer name is restricted to
> a 4 byte integer, unless you change the DRI proto..

For what it's worth, revving DRI proto isn't really that much of a Bad
Thing when both the X server and the clients already need changes, such
as in this case.  Unlike most X protocol which must interoperate between
any server and client in the universe, with DRI protocol the server and
client are always on the same system, and must be upgraded
simultaneously anyway for a change like this.

In fact, it might be desirable to use new protocol so that a mismatched
client won't try to use a new-style handle with old-style DRM or vice
versa (the failure should be more obvious with new protocol).

- Robert

> Authentication hooks for the driver (on x11 driver side) are for a
> single authentication covering all buffers shared between client and
> server, and is done by 4 byte token exchange between client and
> server.  I've not had time yet to look more closely at the
> authentication aspect of ION.
> Those are just things off the top of my head, hopefully someone else
> from X11 world chimes in with whatever else I missed.  But I guess
> most important thing is whether or not it can fit within existing DRI
> protocol.  If it does, then the drivers on client and server side
> could use whatever..
> BR,
> -R
> > Thanks,
> > Sree
> >
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> >
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