Bug#616720: linux-image-2.6-xen-amd64: Feature request -- Serial driver serial8250 as module

[Ian Campbell <ijc@hellion.org.uk>]

On Tue, 2011-03-08 at 13:23 +0100, David Rütti wrote:
> 
>  Hello Bastian 
>  
> > > Please compile serial driver serial8250 as module instead into the
> kernel. 
> > 
> > Please explain why.
> 
> I would like to provide a DomU serial port access according to the
> xen-wiki.
>  
> 
> 
> To have access to the serial port in DomU, we need to prevent Dom0
> from taken hold of this piece of hardware 
> 
> add to /etc/hotplug/blacklist the following modules to exclude from
> being loaded 
> 
> 8250 
> 
> 8250_pnp 
> 
> serial_core 
> 
>   
> 
> domU config: 
> 
> irq = [ 4 ] 
> 
> ioports = [ "3f8-3ff" ] 
> 
> to load the modules in domU. 
> 
>  
> 
> I tried without unload the 8250 driver and starting the domU resuted
> in an IRQ 4 error.

So what you really need is to inhibit the 8250 driver from claiming the
ports/irqs associated with the serial points. I don't think you need to
inhibit the driver loading to do this.

I think this can be done with "8250.nr_uarts=0" on your domain 0 kernel
command line. (I've only ever used =1 myself but I'd expect =0 to work
by extension).

I see /sys/bus/platform/drivers/serial8250/{un,}bind on my systems, so
it's perhaps possible that you can also control this stuff even more
dynamically on a per-port basis too.

Ian.


> 
>  
> 
> Kind regards
> 
>  
> 
> David
> 

-- 
Ian Campbell
Current Noise: Anathema - Thin Air

Government lies, and newspapers lie, but in a democracy they are different lies.