Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driveropt-in

[Jeff Garzik]

Matthew Wilcox wrote:
> On Sat, Jan 12, 2008 at 08:42:48PM -0800, Arjan van de Ven wrote:
> > Wanne bet there'll be devices that screw this up? THere's devices that even screwed
> > up the 64-256 region after all.
>
> I don't know if they 'screwed it up'.  There are devices that misbehave
> when registers are read from pci config space.  But this was never
> guaranteed to be a safe thing to do; it gradualy became clear that
> people expected to be able to read random registers and manufacturers
> responded accordingly, but I don't think you were ever guaranteed to be
> able to peek at bits of config space arbitrarily.

Quite correct...  Reading registers can have all sorts of side effects, 
for example clearing chip conditions.

	Jeff



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