linux-kernel - Re: [PATCH] PCI: boot parameter to avoid expansion ROM memory allocation

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Message-ID: <20080514000702.GA12546@us.ibm.com>
Date:	Tue, 13 May 2008 17:07:02 -0700
From:	Gary Hade <garyhade@...ibm.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Gary Hade <garyhade@...ibm.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] PCI: boot parameter to avoid expansion ROM memory allocation

On Tue, May 13, 2008 at 04:23:55PM -0700, Yinghai Lu wrote:
> On Tue, May 13, 2008 at 3:28 PM, Jesse Barnes <jbarnes@...tuousgeek.org> wrote:
> > > >  There were some lkml/linux-pci visible discussions back in
> >  > >  November-December of last year where I floated the idea
> >  > >  of making PCI expansion ROM memory non-assignment the default:
> >  > >   http://marc.info/?l=linux-kernel&m=119742188215024&w=2
> >  > >   http://marc.info/?l=linux-kernel&m=119689499508369&w=2
> >  > >  I did not hear any objections so I went ahead and submitted
> >  > >  the change which entered mainline at 2.6.25-rc1 but it was
> >  > >  sternly evicted last week because of a reported regression
> >  > >  that it had caused:
> >  > >   http://marc.info/?l=linux-kernel&m=121029093331908&w=2
> >  > >  Attachments to http://bugs.freedesktop.org/show_bug.cgi?id=15523
> >  > >  indicate that a 2.6.25-rc2 x86_64 kernel was being used.
> >  > >
> >  > >  > can we use pci rom in 64 bit kernel?
> >  > >
> >  > >  Sorry, not sure if I understand this question.  I hope the
> >  > >  above answers it.
> >  >
> >  > ok, i think the driver could reload fw in the option rom to reset the
> >  > controlller in pci card.
> >  > i don't think there is other usage for the option rom after OS loaded,
> >  > except option rom contain other run-time code...
> >
> >  On graphics devices it's used for more than just POSTing (in fact POSTing is
> >  the least of its uses these days).  The ROM often contains tables describing
> >  the specific hardware configuration of a given board, including output
> >  information, extra supported modes, etc.
> >
> >  On other devices, it can be used to store default settings (this is common for
> >  SCSI cards iirc, though I'm not sure how much Linux drivers use this info).
> >
> >
> >  > so could disable them all, and use pci-quirks to enable that for the
> >  > device/driver need it.
> >
> >  Since it's probably only big systems that really need the extra address space,
> >  I'd rather to the opposite:  allocate ROM space by default and let a boot
> >  option avoid it.
> 
> that boot option will get rid of that ROM BAR for all devices...
> big system could use several graphical cards that need ROM BAR and
> several cards that don't need ROM BAR.

Correct, not a perfect solution but better than we have right now.

Gary

-- 
Gary Hade
System x Enablement
IBM Linux Technology Center
503-578-4503  IBM T/L: 775-4503
garyhade@...ibm.com
http://www.ibm.com/linux/ltc
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