[Linaro-mm-sig] [RFC] dma-shared-buf: Add buffer sharing framework

Clark, Rob rob at ti.com
Thu Sep 8 22:56:19 UTC 2011

On Thu, Sep 8, 2011 at 3:28 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Thu, Sep 08, 2011 at 12:39:41PM -0500, Clark, Rob wrote:
>> On Thu, Sep 8, 2011 at 10:55 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
>> > On Thu, Sep 08, 2011 at 08:45:43PM +0530, Sumit Semwal wrote:
>> >> On 8 September 2011 19:48, Clark, Rob <rob at ti.com> wrote:
>> >> > actually, all I think we needed was to add 'struct device *'  to
>> >> > get_scatterlist (and maybe doesn't hurt for put)..  I'm not entirely
>> >> > sure why we need create/attach_device?  The create fxn especially
>> >> > seems wrong.. what if you are the 2nd device to import the buffer?
>> >> >
>> >> Ah... I guess I misunderstood your 'it seems like a sane approach' to mean
>> >> you agree with the 2-step process suggested by Daniel :) - my bad!
>> >
>> > On re-reading Rob's response I think there's a misunderstanding. I don't
>> > want a create function in the dma_buf_ops. The create would be a generic
>> > dma_buf subsystem function that (like in the patch) allocates the struct
>> > and properly registers the fd and what not else. The attach_device would
>> > then be the only new function in dma_buf_ops.
>> >
>> > The confusion probably stems from my other proposal to hide these function
>> > pointers behind small inline helpers for the in-kernel api.
>> I guess/assume that what you are trying to get to is a way to
>> differentiate between "I am done DMA'ing to the buffer now, but will
>> likely use it again (ie. feel free to cache the mapping)", and "I am
>> done forever w/ the buffer (don't bother caching)"?
> Hm, no, I haven't really thought much about the release side. dri2/gem
> doesn't have any automatic caching of shared buffers, btw, that's all done
> manually (i.e. in the higher levels like the mesa/ddx drivers) by keeping
> track of recently shared buffers (and hanging onto them for as long as
> possible without creating havoc on the other side).

ok, then I've lost sync.. (ok, I admit to be only having time to read
email for 5 min here and there, which might be contributing to the

what was the purpose of attach() then (which couldn't be accomplished
in the first get_scatterlist())?


> -Daniel
> --
> Daniel Vetter
> Mail: daniel at ffwll.ch
> Mobile: +41 (0)79 365 57 48

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