RE: [Xen-ia64-devel] [PATCH 0/6] Add full evtchn mechanism forxen/ia64

[Alex Williamson <alex.williamson@xxxxxx>]

On Mon, 2006-05-22 at 14:53 +0800, Tian, Kevin wrote:
> >From: Isaku Yamahata [mailto:yamahata@xxxxxxxxxxxxx]
> >It is bad that xen and dom0 accesse to the same UART.
> >This is only what I'm sure about.
> 
> Yes, that's bad which may be the reason why xen/x86 disables serial 
> directly. Ideally that should also apply to xen/ia64 since that option is 
> common in drivers/xen. So I'm not sure why that option doesn't work 
> for ia64. Alex should know more about this area, and it may simply 
> come from a mis-configuration case...

   Configuring the serial console is far more painful than it should be
right now on xen/ia64.  This is due to the fact that xen and xenlinux
both claim the same physical UART.  On xen/x86, the physical UARTs are
hidden from xenlinux using the config option such that only xen talks to
the physical hardware and ttyS0 on xenlinux is actually xencons.
Xen/ia64 leaves the serial driver in place, which allows xenlinux to
claim the physical UART.  We therefore have to disable input in xencons
and play games with assigning xencons to ttyS values outside of what the
serial driver typically claims.

   While not ideal, I think we should take the xen/x86 approach and
disable serial access from dom0.  At some point maybe we can add support
to hide only the physical UART used by xen and allow dom0 to access any
others that might be available.  Such a feature would need to be aware
of both I/O port and MMIO UARTs and handle UARTs described in ACPI
namespace.  Thanks,

        Alex

-- 
Alex Williamson                             HP Linux & Open Source Lab


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