RE: [Xen-ia64-devel] Console investigation.

[Alex Williamson <alex.williamson@xxxxxx>]

On Wed, 2005-12-14 at 17:13 -0800, Magenheimer, Dan (HP Labs Fort
Collins) wrote:
> Alex --
> 
> So after recent changes in xen-unstable, can I enable
> CONFIG_XEN_CONSOLE_INPUT, leave CONFIG_SERIAL_8250_ACPI
> enabled in the xen0 and xenU config files and, possibly,
> enable CONFIG_VT in xenU?  And, if so, do I need to specify
> something different on Xen's boot line?
> 
> Or is this still work in progress?

  Until we figure out how to hide a UART, it's still somewhat of a work
in progress.  We should now be able to shift the xenU console to a port
that doesn't interfere with either CONFIG_VT or CONFIG_SERIAL_8250*.
For instance, booting xenU with "xencons=ttyS8 console=ttyS8" makes it
use a serial port (avoiding vt collision) above the range claimed by the
8250 driver.  Port ttyS63 might be a good defacto port to use.

   BTW, I was trying to figure out where/how the xenU config file info
gets consumed wrt creating a boot command line for the domain.  I'd
really like to get away from the hard coded setup we have now, but I
haven't been able to piece together how to get that data.  Anyone have a
clue?

   On xen0, we still have the problem of hiding the console UART.
Disabling CONFIG_SERIAL_8250_ACPI is an easy hack, but only works on
some boxes with very specific console setups.  We could remove
CONFIG_SERIAL_8250 entirely from the xen0 config, which also solves the
problem, but will make non-console UARTs inaccessible.  This is what x86
does now, so maybe it's not a terrible solution.

   Is a boot time option to xen0 really the best way to hide the port?
I'm concerned about upstream accepting such a solution.  I'm also hoping
someone is going to speak up with a cool trick of how we can hide a
given MMIO address from a domain and trap it's accesses.  I know
performance is a high priority, but anytime we talk to MMIO, there's
already a huge performance penalty.  A lightweight trap might be in the
noise.  Thanks,

        Alex

-- 
Alex Williamson                             HP Linux & Open Source Lab


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