linux-kernel - Re: Problems with serial interrupts with IPMI 2.0 SoL

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Date:	Thu, 10 Dec 2009 21:55:50 -0200
From:	Mauro Carvalho Chehab <mchehab@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Keir Fraser <keir.fraser@...citrix.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Problems with serial interrupts with IPMI 2.0 SoL

Em Thu, 10 Dec 2009 13:45:54 -0800
Jeremy Fitzhardinge <jeremy@...p.org> escreveu:

> Hi,
> 
> I'm using a system with an embedded IPMI 2.0 BMC which provides SoL 
> (Supermicro X8SIL-F).  This works fine under Linux (fully interrupt 
> driven), but fails for Xen as it appears to not be sending interrupts; 
> it works OK if I set the driver to polling mode.
> 
> I'm assuming the Xen is tickling some bug in the emulated 16550.  The 
> Linux driver has a couple of pieces of code to explicitly work around 
> bugs in the Intel AMT SoL implementation, but I don't think they're 
> coming into play here (because there are no Intel SoL PCI devices on 
> this system to trigger the NO_TXEN_TEST flag).
> 
> I'm wondering if you have any pointers or suggestions about more subtle 
> problems?

If you don't hit NO_TXEN_TEST flag, you'll be loosing interrupts, as the
emulation of 16550 is not perfect.

As far as I remember, interrupts take too long to happen with the emulated
16550, when comparing with a normal serial.

-- 

Cheers,
Mauro
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