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

Jeff Garzik
2008-01-13T06:43:46Z

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