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RE: [Xen-devel] "outgoing" serial port

To: "Rik van Riel" <riel@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] "outgoing" serial port
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Mon, 21 Feb 2005 09:39:17 -0000
Cc: <ian.pratt@xxxxxxxxxxxx>
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Thread-topic: [Xen-devel] "outgoing" serial port
 

> I've got the serial console on my Xen system working reliably
> now, since Keir's patch went in.   However, I can't find a way
> to use the other serial port to connect to the serial console
> on the other system under my desk.
> 
> Loading the 8250 serial driver doesn't work, since the serial
> console already takes up some of the resources that the 8250
> serial driver wants to claim.
> 
> I'm wondering what the most acceptable way would be to resolve
> this problem...

I guess there are two options:
 * have Xen virtualize both ports on the UARTS, and hence have a ttyS1.
Since people woould generally want to use the 2nd port for fancy things
like modems etc it would probably need to be quite a full emulation
rather than just tx/rx.

 * have Xen use the iobitmap to protect access to COM1, while allowing
the guest to use COM2. What does the Linux UART driver do if COM1
appears not to exist, does it still probe for COM2 (I guess so). Also,
we'll have to think through how to have ttyS0 driven by xencons, and
ttyS1 by the 8250 driver.

Ian


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