On Thu, 13 Feb 2014 13:48:40 -0600, Josh Cartwright <jo...@codeaurora.org>
wrote:
> On Tue, Feb 11, 2014 at 09:27:36PM +0100, Tomasz Figa wrote:
> > On 11.02.2014 21:19, Josh Cartwright wrote:
> > >On Tue, Feb 11, 2014 at 09:04:21PM +0100, Tomasz Figa wrote:
> > > >On 11.02.2014 21:02, Benjamin Herrenschmidt wrote:
> > > > >On Tue, 2014-02-11 at 19:01 +0000, Grant Likely wrote:
> > > > > > > except that the former IMHO better suits the definition of memory
> > > > > > > region, which I see as a single contiguous range of memory and
> > > > > > > can be
> > > > > > > simplified to have a single reg entry per region.
> > > > > >
> > > > > > My point is rather if multiple reg tuples are found in a reserved
> > > > > > memory
> > > > > > node, the kernel must respect them and reserve the memory. I'm not
> > > > > > arguing about whether or not that makes for a good binding.
> > > > >
> > > > > agreed.
> > > >
> > > > My point is why, if the binding defines that just a single tuple should
> > > > be
> > > > provided.
> > >
> > > FWIW, the usecase I had mentioned in reply to Grant in the patch 5/5
> > > thread [1] could make use of this. The shared memory region is split
> > > into a main chunk and several "auxiliary" chunk, but collectively these
> > > regions all share the same heap state.
> > >
> > > Josh
> > >
> > > 1: http://lkml.kernel.org/r/20140205192502.go20...@joshc.qualcomm.com
> >
> > The use case seems fine, but I believe it could be properly represented in
> > device tree using multiple single-reg regions as well, unless the consumer
> > can request a block of memory that crosses boundary of two sub-regions
> > specified by reg entries of single region.
>
> I could probably make a only-one-reg-entry policy work for me, but it
> makes things a bit more awkward. I'd lose the ability to describe
> "this set of regions need to be logically handled together" directly in
> the reserved memory node, and would need to push it up a layer.
>
> reserved-memory {
> smem: smem {
> reg = <...>;
> };
> aux1: auxiliary1 {
> reg = <...>;
> };
> aux2: auxiliary2 {
> reg = <...>;
> };
> ...
> };
If the regions are used for different purposes, it makes sense I think
to have a separate node for each. Multiple tuples would make more sense
for something like valid DMA regions for a broken device that can only
DMA into a few windows; you could have one tuple per window within a
single node.
It would be possible to collect multiple associated nodes under one
parent node which in turn has reserved-memory for its parent:
reserved-memory {
ranges;
reserved-group {
ranges;
smem: smem {
reg = <...>;
};
aux1: auxiliary1 {
reg = <...>;
};
aux2: auxiliary2 {
reg = <...>;
};
};
...
};
g.
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