Subject: Re: [PATCH 1/2] [RESEND] PCI: read revision ID by default
From: Arjan van de Ven <arjan@infradead.org>
To: "Kok, Auke" <auke-jan.h.kok@intel.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, gregkh@suse.de,
       linux-pci@atrey.karlin.mff.cuni.cz, linux-kernel@vger.kernel.org,
       grundler@parisc-linux.org, davem@davemloft.net, davej@redhat.com
In-Reply-To: <46800E35.9030209@intel.com>
References: <20070625031918.4711.2705.stgit@localhost.localdomain>
	 <20070625100109.35b4c327@the-village.bc.nu>  <46800E35.9030209@intel.com>
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Organization: Intel International BV
Date: Mon, 25 Jun 2007 12:48:29 -0700
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On Mon, 2007-06-25 at 11:49 -0700, Kok, Auke wrote:
> Alan Cox wrote:
> > On Sun, 24 Jun 2007 20:19:18 -0700
> > Auke Kok <auke-jan.h.kok@intel.com> wrote:
> > 
> >> Currently there are 97 occurrences where drivers need the pci
> >> revision ID. We can do this once for all devices. Even the pci
> >> subsystem needs the revision several times for quirks. The extra
> >> u8 member pads out nicely in the pci_dev struct.
> >>
> >> Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
> > 
> > Seems worth caching yes. Care needed changing the other uses however
> > that the revision isn't changeable on the hardware in some magic fashion.
> 
> if that happens the device could also change pci ID... I don't think we can 
> guard against that kind of abuse anyway. While this is perfectly possible (e.g. 
> network cards carrying this info in their eeproms), we should still be OK with 
> the core patch, but the device driver itself needs to pull the information 
> manually from the device using the pci_get_config_byte() method.


the other thing btw is that this approach allows us to use quirks and
the like to fix up "crap".

Maybe a good rule-of-thumb (and as with any other rule of thumb there
are exceptions): Drivers should NEVER touch the standard part of PCI
config space without going through a specific PCI layer API for the
value they want.


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