Re: [RFC 3/6] dt/bindings: Add bindings for Tegra20/30 NOR bus driver

[Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Mon, Jul 25, 2016 at 09:59:34PM +0200, Mirza Krak wrote:
> 2016-07-25 16:15 GMT+02:00 Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>:
> > On Mon, Jul 25, 2016 at 03:16:28PM +0200, Mirza Krak wrote:
> >> 2016-07-25 13:30 GMT+02:00 Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>:
> >> >
> >> > I would've expected this to require some sort of infrastructure to allow
> >> > devices connected to the GMI controller to acquire the bus via some API
> >> > to select their chip.
> >>
> >> Yes, ultimately you would need some sort of infrastructure to allow
> >> devices to acquire the GMI bus if you want to solve this in software.
> >> But at the moment I do not see such an infrastructure in place, and is
> >> it feasible to add one specifically for the GMI controller? If one
> >> such infrastructure was in place we would need to modify all the
> >> drivers that want to use to include Tegra specific infrastructure to
> >> access the GMI bus?
> >>
> >> Since my knowledge is limited it hard for me to comment on this, maybe
> >> there is a simple way of doing this?
> >
> > I don't think there's a simple way to do this. In order to properly
> > implement it we'd need to implement a generic infrastructure for chip
> > selects so that drivers such as the one for your CAN controller can be
> > written without tying them specifically to the Tegra GMI controller.
> >
> > From what you and Jon were saying it sounds like the drivers are
> > completely agnostic of any chip-select, so conversion won't be easy.
> > But technically if these chips take a chip-select as input then it's
> > always possible to hook them up to a controller that doesn't do this
> > automatic translation of address to chip-select, so eventually some
> > setup is bound to come along where they'd need explicit chip-select
> > handling as well.
> >
> > I don't think it's fair to require you to implement this infrastructure
> > if you don't actually need it. At the same time I want to be cautious
> > and make sure we keep the driver and binding flexible enough to allow
> > us to implement explicit chip-selects should we later need them.
> >
> > Thierry
> 
> One thing that should be noted, and that is the GMI controller also
> supports a DMA master mode (feature for the future?).
> 
> I do not really know how this effects the binding we are discussing
> but wanted to put it out there.

Yes, that had occurred to me as well. I don't really have any good ideas
on how to use that other than to implement it as a DMA engine driver and
have drivers use those, if available.

But I don't think we have to worry about it right now. If we ever need
it, the binding can be extended in a backwards-compatible way.

Thierry

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