linux-kernel - Re: [patch 2/2] 8250_pnp: register x86 COM ports at the conventional ttyS names

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Date:	Thu, 17 Jan 2008 00:34:05 +0100
From:	Rene Herman <rene.herman@...access.nl>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	7eggert@....de, Bjorn Helgaas <bjorn.helgaas@...com>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	Russell King <rmk+serial@....linux.org.uk>,
	Jeff Garzik <jeff@...zik.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [patch 2/2] 8250_pnp: register x86 COM ports at the conventional
 ttyS names

On 16-01-08 21:42, H. Peter Anvin wrote:

> Bodo Eggert wrote:
>> 
>> BTW1: These addresses may be used to detect ports on non-standard 
>> addresses, but unfortunately they don't tell the IRQ.
>> 
>> BTW2: When I submitted a patch using the BIOS data area, I was told 
>> that it might not exist on systems booting from non-PC firmware. This 
>> claim was not yet backed with any knowledge, nor did anybody suggest a 
>> way to detect this situation.
> 
> This is, of course, true.  It doesn't exactly help that some (most?) 
> non-PC firmware at least mimic the BIOS data area.
> 
> In this particular case, there is some minor sanity-checking that can be
> done: the values should be nonzero and aligned 8.

The number of places expected to contain something sensible should I believe 
first be verified at 0x410 -- the equipment word. Bits 11-9 (0x0e00) should 
be the number of serial ports, 0 to 4 (so 5-7 is also a sanity check) and if 
BIOSes can be expected to zero out the non-used base-addresses (at 0x400, 
0x402, 0x404, 0x406) that's another sanity check. Don't know if they can 
though...

Rene.
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