Re: [XenPPC] [rfc] Serial discovery.

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

On May 1, 2006, at 11:45 AM, Hollis Blanchard wrote:

> On Mon, 2006-05-01 at 11:23 -0400, Jimi Xenidis wrote:
> > Right now our serial device is assumed to be hanging off an ISA bus
> > (hardcoded address) at an offset (also hardcoded).
> > Neglecting the IOMMU, the only devices that we are interested is
> > console.
> > Right now we are restricting console to a UART, and have no plans to
> > support a framebuffer,ps/2,ADB,USB stuff tho it is possible (except
> > for USB :)).
> I assume you mention these because xen/drivers/char/console.c uses the
> IO accessors for VGA, e.g. inb(0x3da). Why should we write those off?
I don't want to write them off at all, we are just not focused on them.

> > Anyway, rather defining a bus+offset I think we should just keep an
> > absolute address for the UART.
> What problem does this solve?
Some UARTs will not be the ISA (like on all apple machines), when all  
we are interested is where the console device is.
The isa_base+offset logic could be simulated but, but why?

> (It looks like ns16550.c may work with this change, but note the logic
> in e.g. ns16550_init_preirq and ns_read_reg. The behavior of that  
> driver
> would change.)
It does work, its how we got it to work first, but I was convinced to  
use an ISA base, and I'm beginning to believe that it was the wrong  
way to do it.
> If the issue is that you want to use inb/outb in a Zilog driver,
You wish to make inb/outb ISA only interfaces?

> please
> use ioremap (even though it's a no-op) and readb/writeb instead, like
> ns16550.c.
agreed.
-JX

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