[Ksummit-2013-discuss] ARM topic: Is DT on ARM the solution, or is there something better?

[Sascha Hauer]

On Thu, Oct 24, 2013 at 10:17:33AM +0200, Thierry Reding wrote:
> On Thu, Oct 24, 2013 at 10:06:24AM +0200, Sascha Hauer wrote:
> > On Wed, Oct 23, 2013 at 12:54:35PM -0600, Jason Gunthorpe wrote:
> > > On Wed, Oct 23, 2013 at 08:30:42PM +0200, Richard Cochran wrote:
> > > > On Wed, Oct 23, 2013 at 12:25:02PM -0600, Jason Gunthorpe wrote:
> > > 
> > > > > On ARM the package of 'stuff' can very reasonably include dtb. Distro
> > > > > scripts can package modules+DTB+vmlinuz into something the bootloader
> > > > > can understand. (The next pain point will be to standardize that)
> > > > > 
> > > > > The DTB doesn't have to be 'outside' the distro/kernel to give users a
> > > > > seamless upgrade experience.
> > > > 
> > > > How can a distro possibly provide me a DTB?
> > > > 
> > > > They don't know what hardware I am using. Only I know that.
> > > 
> > > I'm not sure what you are asking? Treat DTBs like kernel drivers. If
> > > you make hardware and you want distros to run on it, you have to
> > > provide the DTB for that hardware to mainline+distros.
> > > 
> > > Remember, there are two ways to view DTB:
> > >   a) It comes from the firmware and you have to live with whatever
> > >      crap the firmware does
> > >   b) It comes from the kernel, must match the kernel, and we don't
> > >      have to tolerate crap in the DTB.
> > 
> > c) It comes from the firmware and is at least good enough to bring up a
> >    kernel to install a better devicetree.
> 
> That's an interesting new view. And I think that makes a lot of sense
> because it matches the product cycle pretty well. Typically I wouldn't
> expect an upstream kernel to be fully featured when first shipped in a
> product, for all the known reasons, but it should be possible to come
> up with stable bindings good enough to perhaps boot to a command-line
> prompt and have some way of accessing other files (network, block
> device, ...).
> 
> Then again you could argue that the bootloader should be able to update
> itself (and the DTB while at it).

barebox/u-boot usually can do this, but I think distributions can
provide a much better and more consistent user interface. Also it offers
a distribution to provide a way to update the devicetree. Otherwise
the distributions can only say: See your boards documentation how to update
the devicetree.

Sascha

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