linux-kernel - Re: Why do we probe option roms at 2K boundaries?

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Message-ID: <20090716001016.489fa970@lxorguk.ukuu.org.uk>
Date:	Thu, 16 Jul 2009 00:10:16 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Alan Cox <alan@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Hans de Goede <hdegoede@...hat.com>
Subject: Re: Why do we probe option roms at 2K boundaries?

> interrogating a data structure stored in option-rom memory.  My initial
> implementation involved blindly scanning from c0000 to f0000 in 512 byte
> increments.  Neil and others pointed out that this may not be a safe

It isn't safe. If you hit certain ISA devices your system will drop dead.
OTOH I doubt anyone has an intel matrix raid controller and a WD80x3 on
the same box ;)

> Recently Hans has been working to get Fedora up and running on a recent
> Intel software RAID platform and noticed that the option-rom is no
> longer visible with the 2K aligned scan.  I.e. he needed to make the
> following changes to the mdadm probe_roms() routine:

Option ROMs should be 2K aligned. Is your data structure part of a ROM or
an actual ROM header ?

> Is this safe?  Should the kernel be updated as well?  I am assuming that
> you were the one that originally introduced the 2K aligned scan with
> this commit from the historical git:

Actually I don't think that was me, don't remember it anyway.

The man to bug at the moment on ROM magic is probably H Peter Anvin
however.

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