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[Xen-users] dom0 serial port usage

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] dom0 serial port usage
From: Ferenc Wagner <wferi@xxxxxxx>
Date: Tue, 18 Mar 2008 17:38:41 +0100
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Hi,

my physical machine (Dell PE2650) has two serial ports, the
/proc/tty/driver/serial output looks like this under a non-XEN Linux
kernel:

serinfo:1.0 driver revision:
0: uart:16550A port:000003F8 irq:4 tx:2761 rx:2766 CTS|CD|RI
1: uart:NS16550A port:000002F8 irq:3 tx:58353 rx:2986 RTS|CTS|DTR|DSR|CD|RI
2: uart:16550A port:0000EC80 irq:177 tx:0 rx:0 CTS|DSR|CD
3: uart:unknown port:000002E8 irq:3

I don't know what the third line is, but the first two work all right.

Now, I'm trying to use both from my DOM0 running Linux 2.6.18-xen,
booting by GRUB like this:

title           Xen 3.0.3-1-i386-pae / Debian GNU/Linux, kernel 2.6.18-6-xen-686
root            (hd0,0)
kernel          /xen-3.0.3-1-i386-pae.gz com1=19200,8n1 com2=57600,8n1 
console=vga dom0_mem=256M
module          /vmlinuz-2.6.18-6-xen-686 root=/dev/mapper/xen2ha-root ro 
console=tty0 console=ttyS1,57600n8r noresume xencons=off
module          /initrd.img-2.6.18-6-xen-686
savedefault

Still, neither is usable.  I'm probably misunderstanding XEN's serial
port emulation.  How should I go about this?

I'm almost there by using com2=auto,8n1 console=com2L,vga and
xencons=ttyS16, which makes possible loading 8250.ko in DOM0 to access
ttyS0.  However, that ttyS0 is losing lots of characters under very
slight loads, which made me think there must be a better solution.
Is there?

Also, is it possible to use hardware flow control on the emulated
ports?  The console is losing characters all the time, too...
-- 
Thanks,
Feri.

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