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    SubjectRe: [patch 3/6] add pmem driver
    On Mon, 2009-09-14 at 15:19 -0700, Brian Swetland wrote:
    > On Mon, Sep 14, 2009 at 3:06 PM, Daniel Walker <> wrote:
    > > On Mon, 2009-09-14 at 23:58 +0200, Pavel Machek wrote:
    > >>
    > >> This adds android pmem driver, one of dependencies of camera driver.
    > >
    > > I wouldn't even both with this one .. There's no way it could ever go
    > > into mainline .. According to the android developers the camera , and
    > > the frame buffer driver should work without it anyway..
    > The latest camera driver should work without pmem (or be fixable to do
    > so -- I forget if that's done yet).
    > The framebuffer itself does not need pmem, but pmem is used heavily by
    > the android userspace on dream/magic for hardware compositable
    > surfaces (since the 2d compositor requires physically contiguous
    > memory).
    > Is there a general linux kernel solution for managing large (1-8MB+)
    > chunks of physically contiguous memory that needs to be shared between
    > kernel and userspace for media operations? This is a very common
    > problem with these SoCs -- the a/v subsystem and/or GPU don't have
    > scatter/gather or MMU support and as a result we need to carve out
    > memory for their use and provide some way for userspace to manipulate
    > it.

    After out last conversation I found the the system calls
    splice/vm-splice .. I don't know a great deal about those system call,
    but from what I read that sounded like it would be the appropriate way
    to transfer memory between two kernel drivers (i.e. camera to
    framebuffer) ..

    As for sharing it with userspace, I haven't really researched that
    enough to give a good answer. I would think you could build something
    into the camera driver that would expose the memory to userspace
    temporarily then the camera could reclaim the memory later.


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