[U-Boot] [RFC] ns16550: Add support for AUX regs usage on some ARC SoCs

[Alexey Brodkin <Alexey.Brodkin@synopsys.com>]

Hi Simon,

On Thu, 2018-02-22 at 10:29 -0700, Simon Glass wrote:
> Hi Alexey,
> 
> On 22 February 2018 at 09:23, Alexey Brodkin
> <Alexey.Brodkin@synopsys.com> wrote:
> > Hi Simon,
> > 
> > On Thu, 2018-02-22 at 09:17 -0700, Simon Glass wrote:

[snip]

> > > I think a separate driver might be better, unless we want to make the
> > > read/write interface go through regmap or similar?
> > 
> > But in case of ARC's AUX regs portmap won't help because those AUX regs are
> > couldn't be mapped - that a completely different address space and we may
> > only access them via dedicated instructions (LR vs LD and SR vs ST).
> 
> Well...
> 
> 1. With a separate driver, you can do whatever you want :-) I know it
> introduces code duplication though...

Exactly I hate to introduce another driver which will be 99,9% the same
as an existing one and then we'll need to care of it as well.

> 2. With regmap you can add your own regmap driver, and again do
> whatever you want. I can help with that if it sounds attractive

Ok so I took a look at regmap in Linux kernel and indeed that
will solve our problem: we'll have a regmap-mmio.c and regmap-arcaux.c
with appropriate implementation of accessors but I'm not really sure
it worth the trouble. Or your idea was to move all the different #ifdefs from
serial_{in|out}_shift() to the corresponding regmap implementations such that
we have something like below:
 regmap-mem32-le.c
 regmap-mem32-be.c
 regmap-portmapped.c
 etc
?

Regards,
Alexey