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

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Lundi 22 Mai 2006 16:12, Alex Williamson a Ãcrit :
> 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,
Modifying ACPI to hide an UART seems to be very hard...

Just an idea: if UART is used by Xen, it should reverse the interrupt line 
(unless shared...)  In this case, Linux shouldn't be allowed to register an 
handler for this IRQ and should fail to use the UART.  Right ?

Tristan.

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