Re: [RFC PATCH] PCI MMCONFIG: add validation against ACPI motherboard resources

Robert Hancock
2007-05-23T00:54:23Z

Jesse Barnes wrote:
> On Tuesday, May 22, 2007, Robert Hancock wrote:
>> Eww. I don't see where we disable the decode at all while we probe the
>> BARs on the device. That seems like a bad thing, especially with the way
>> we probe 64-bit BARs (do the low 32 bits first and then the high 32
>> bits). This means the base address effectively gets set to 0xfffffff0
>> momentarily, which might cause some issues.
>
> I'm a bit shocked that things work as well as they do without the
> disabling...
>
>> I'd try adding some code inside pci_setup_device (drivers/pci/probe.c)
>> to disable PCI_COMMAND_IO and PCI_COMMAND_MEMORY on the device when
>> probing devices with the standard header type and then restoring the
>> previous command bits afterwards, and see what effect that has. It'll be
>> interesting if it does, since obviously it seems to work as it is with
>> non-MMCONFIG access methods. Maybe the base address being set like that
>> interferes with MMCONFIG access itself somehow?
>
> I tried that, and it seems to get past probing the graphics device at
> least, but it hangs a bit later. It could be that the enable/disable I
> added wasn't correct though, I didn't check to see which one I should
> disable in the command word, which may be a problem (just disabled them
> both every probe). I'll try again with more precise enable/disable
> semantics.

It'd be interesting to see at what access it ran into trouble next, at
least if it's consistent. Could be that some device doesn't like having
the decode disabled..

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Robert Hancock Saskatoon, SK, Canada
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