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

[Oskar Senft]

Done. I submitted just a v2 of the patch alongside the other bits and
pieces that are required to make this work.

Let me know if that works for you or if there's anything that should be
changed.

Oskar.

On Sun, Jul 28, 2019 at 11:02 PM Andrew Jeffery <andrew at aj.id.au> wrote:

>
>
> On Mon, 29 Jul 2019, at 11:51, Oskar Senft wrote:
> >
> > 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"?
>
> It might be better to add a property to the UART DT node that references
> the SCU syscon by phandle, that way you don't need to muck around
> with compatible names for the SCU syscon.
>
> Andrew
>
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