[PATCH] drivers/tty/serial/8250: Make Aspeed VUART SIRQ polarity configurable

[Oskar Senft]

Hi Jeremy

Somewhat offtopic, but are you sure you want to enable the SuperIO
> device?
>
No :-D I'm aware of CVE-2019-6260. I just listed it as a potential source
of SIRQs.


> >  The VUART is covered by this code and we don't have a PUART driver
> > yet.
> >
> > It might make sense to have this as a global setting which each driver
> > could read. But wouldn't this be an exercise for the future where we
> > actually have a second device? I don't think the Aspeed currently has
> > any other devices that could generate a SIRQ (except for the PUART for
> > which there's no driver).
>
> We have a bunch of SIRQ sources that we use (on OpenPOWER platforms) -
> the BT interface, the KCS interface, the UARTs, and the mbox hardware.
> It's not just the VUART/PUART :)
>
Interesting. From what Aspeed explained, the SIRQ polarity for UARTs is
inverted to that for other devices. I haven't looked into how other devices
work, to be honest. Do we set the polarity there explicitly?


> > Having said that, ideally I'd like the SIRQ polarity to be auto-
> > configured from the LPC/eSPI HW pin strap anyway. I have the code for
> > that almost done. Maybe we shouldn't even have the sysfs interface for
> > it and I should strip that out?
>
> Yeah, I think I agree with that. The only downside is that the
> individual drivers will now need to poke at the SCU to query the
> LPC/eSPI configuration. If you can find a nice way to do that, then that
> sounds like the best approach. Can you query it through the parent bus
> perhaps?
>
I'm experimenting with this:
syscon_regmap_lookup_by_compatible("aspeed,ast2500-scu");

I'll need to think on how to make this work on both ast2400 and ast2500,
though. I actually need to have a look at the ast2400 data sheet wrt. VUART
registers, too!

The structure is this:
apb {
  syscon {
    ...
  }
  vuart {
    ...
  }
}

So the vuart is a sibling of syscon, which holds the registers. I guess
I'll have to go with "by_compatible"?

Oskar.
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