linux-kernel - Re: [PATCH 1/2]: serial8250: Use native_io

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Message-ID: <20100317130159.23d1103f@linux.intel.com>
Date:	Wed, 17 Mar 2010 13:01:59 +0000
From:	Alan Cox <alan@...ux.intel.com>
To:	Simon Kagstrom <simon.kagstrom@...insight.net>
Cc:	x86@...nel.org, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	akpm@...ux-foundation.org, hpa@...or.com
Subject: Re: [PATCH 1/2]: serial8250: Use native_io_delay on the x86

On Wed, 17 Mar 2010 13:30:50 +0100
Simon Kagstrom <simon.kagstrom@...insight.net> wrote:

> Port 0x80 is not safe to use on all x86 boards (see
> arch/x86/kernel/io_delay.c), so use native_io_delay instead.
> 
> Signed-off-by: Simon Kagstrom <simon.kagstrom@...insight.net>

native_io_delay() won't work if the system is being run with no delays.
The I/O cycle isn't for the delay but to force the bus signals. So in
various modes (paravirt, udelay, no delay) the native_io_delay won't
actually do what is required.

I'm actually surprised you hit this path and if anything the right fix
is to avoid hitting this kind of probing in the first place.


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