[linux-sunxi] Re: [PATCH 4/4] simplefb: add clock handling code

[Thierry Reding]

On Tue, Sep 30, 2014 at 06:39:28PM +0100, Mark Brown wrote:
> On Tue, Sep 30, 2014 at 07:09:24AM +0200, Thierry Reding wrote:
> > On Mon, Sep 29, 2014 at 04:55:17PM +0100, Mark Brown wrote:
> 
> > > So long as we're ensuring that when we don't start supporting resources
> > > without DT additions or at least require DT additions to actively manage
> > > them (which can then include simplefb hookup) we should be fine.
> 
> > I'm not sure I understand what you mean. If we add a driver for the PMIC
> > that exposes these regulators and then add a DT node for the PMIC, we'd
> > still need to fix the firmware to generate the appropriate DT properties
> > to allow simplefb to enable the regulators.
> 
> No, you don't.  It's only if you start describing the regulators in the
> PMIC in DT that you run into problems.  Unconfigured regulators won't be
> touched.

Okay, that's what I meant. It seems rather odd to add a PMIC DT node but
omit the description of the regulators that it exposes. Unless the
regulators are truly unused, as in not connected to any peripherals.

> > So unless firmware is updated at the same time, regulators will get
> > disabled because they are unused.
> 
> That won't happen unless the regulators are explicitly described, if
> they are described as unused then this will of course happen.

With described as unused you mean they have a node in DT, so constraints
are applied and all that, but no driver actually uses them?

The fundamental issue is that if we start describing simplefb nodes with
an incomplete set of resources then we're bound to run into problems
where it'll break once these new resources are described in the DTS. If
the simplefb node was described in the DTS then this would be less of a
problem because the resources could be added to the simplefb node at the
same time.

However given that simplefb is supposed to be generated by firmware this
is no longer possible. It will inevitably break unless you upgrade the
DTB and the firmware at the same time. And it was already decided long
ago that upgrading the firmware should never be a requirement for
keeping things working.

I don't see any way to prevent that other than ignoring the resources in
simplefb completely.

Thierry
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