Re: [Xen-ia64-devel] consoles, iosapics, and device interrupts

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Vendredi 18 Novembre 2005 16:52, Alex Williamson a écrit :
> On Fri, 2005-11-18 at 13:52 +0200, Tristan Gingold wrote:
> > Just be to clear:  there are currently 3 outputs because there are 3
> > consoles: * hpsim cons.
> > * Xen console.
> > * Linux serial.
> > If Xen console is used as input too, you have to disable Linux serial
> > console.
>
>    Right, that's what I'm hoping we can get to since that matches x86
> and I believe it's the only way to get the ^A switching between xen and
> dom0.  It would be nice to hide the physical UART the Xen console uses
> from xenlinux... not sure how best to do that.
>
> > >       * IOSAPICs are parsed late in the hypervisor bootup.  There's a
> > >         timing issue with setting up the RTE at the right point in the
> > >         boot.  We can call ns16550_init() more than once for a port,
> > > but that's pretty ugly.
> >
> > I don't agree.  The serial output is enabled early using pooling. 
> > Interrupts can be enabled later, after parsing IOSAPICS and when
> > interrupts can be enabled.
>
>    AFAICT, ns16550 only outputs a character at a time, so interrupt vs
> polling doesn't really come into play for early output.  The problem
> though is how do we get the irq data back into ns16550?  We have to call
> acpi_register_gsi() to translate the PCDP provided GSI to an irq vector.
> That can only be done after acpi_boot_init() finds the IOSAPICs in
> late_setup_arch().  We certainly don't want to go blind (no console)
> until most of the way through late_setup_arch().  Thus we need some way
> to get an output console working early, then register the IRQ later.  I
> don't know how to do that cleanly.
I don't understand here.  This is already how it works: the console first 
works by polling, then the IRQ *might* be enabled later.


Tristan.


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