Re: [Ksummit-discuss] [TECH TOPIC] mobile phones

[Sebastian Reichel <sre@kernel.org>]

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Hi,

On Wed, Jun 28, 2017 at 10:27:22PM +0200, Pavel Machek wrote:
> > > Oh, another major piece is DSP coprocessor that is there. Unlike
> > > graphics, we don't even know how support for it should like.
> > 
> > https://www.kernel.org/doc/Documentation/remoteproc.txt
> > 
> > config OMAP_REMOTEPROC
> > 	tristate "OMAP remoteproc support"
> > 	[...]
> > 	help
> > 	  Say y here to support OMAP's remote processors (dual M3
> > 	  and DSP on OMAP4) via the remote processor framework.
> > 
> > 	  Currently only supported on OMAP4.
> > 
> > 	  Usually you want to say Y here, in order to enable multimedia
> > 	  use-cases to run on your platform (multimedia codecs are
> > 	  offloaded to remote DSP processors using this framework).
> > 
> > 	  It's safe to say N here if you're not interested in multimedia
> > 	  offloading or just want a bare minimum kernel.
> > 
> > I have been told by some Nokia people (I do not remember who it
> > was, possibly Sakari), that the DSP is not that powerful and any
> > calculation should also be possible on CPU (wasting a bit of
> > energy).
> 
> Ok, we probably don't care about DSP, but lets say we had really
> fast DSP or really cared about power.
> 
> We'd need remoteproc. Sure. But that has no interface for userland,
> right?

remoteproc is only for start/stop + fw loading. The actual
communication is done using rpmsg, which does not yet have a
userspace API afaik.

> So we'd need to introduce interface for userland... fine.
> 
> And then we'd need cross-compilers for the DSP used. Ok.

Yes. As far as I know there is currently no open source toolchain
for the TI DSP.

> And then we'd need to split mpg123 to CPU and DSP parts, and modify it
> so that it can run the DSP parts using remoteproc, when available?
> 
> That starts to be ... complex, with changes all over the system :-(.

With little gain expected on N900...

-- Sebastian

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