[PATCH RFC v1 1/2] documentation/iommu: Add description of Hisilicon System MMU binding

[arnd@arndb.de (Arnd Bergmann)]

On Monday 16 June 2014 19:26:45 Will Deacon wrote:
> On Mon, Jun 16, 2014 at 06:25:35PM +0100, Arnd Bergmann wrote:
> > On Monday 16 June 2014 17:45:17 Will Deacon wrote:
> > > On Mon, Jun 16, 2014 at 05:42:10PM +0100, Arnd Bergmann wrote:
> > > > We have to migrate the driver to the new binding anyway, it may be
> > > > a bit painful, but there are not really any users yet so there
> > > > is a chance we can remove the nonstandard code at some point,
> > > > perhaps in a few years.
> > > 
> > > The only way I see this working is if we kill the existing binding and move
> > > exclusively to the new one. I'm actually ok with that (we have no in-tree
> > > users), but it needs to happen ASAP in my opinion, otherwise we increase the
> > > window where the old binding can be adopted.
> > 
> > I agree. I was hoping to get the generic binding ready for 3.16, but that
> > didn't happen. Maybe we can add a small patch to the binding to explain
> > that it will change in the future.
> 
> Perhaps, but saying "don't use this" isn't much better than just ripping out
> the support altogether. That said, I won't object to a patch adding a big
> fat warning to the current binding docs if it dissuades people from using
> what we currently have.

Ok.

> > > Note that the next version of the ARM SMMU (v3) is considerably different to
> > > the current architecture, so a new driver (using the new bindings) will be
> > > required.
> > > 
> > > This actually opens a wider question: if we don't have an in-tree user for a
> > > device-tree binding, do we consider that binding to be unused?
> > 
> > Not in general, but often. We don't require dts files to be in the kernel,
> > so we have to apply a bit of common sense. If anyone knows of out-of-tree
> > users of the binding that are actually working with upstream kernels,
> > we need a migration path. Anything that also requires out-of-tree kernel
> > patches however is something we don't have to worry about.
> 
> Ok. If Thierry's binding gets in for 3.17, then I'll try to convert the ARM
> SMMU driver over to it for 3.18 providing we don't grow any in-tree users of
> the existing binding in the meantime (or 3.17 depending on how early it gets
> queued).
> 
> Sound fair?

Sounds good. Let's make sure we get this done quickly now. I think there
isn't much controversy left with the binding, though this particular one
has been tough in the past.

	Arnd