On Wed, Sep 26, 2007 at 03:20:40PM -0700, Jesse Barnes wrote:
Yes, nobody is arguing that moving the BAR around is unsafe, but generally
it's the less of two evils.
The major problem here is that with IO and MEM bits cleared in the command
register you disable *all* address decoders on the device, not just ranges
that have respective BARs. At least this behaviour is required by PCI spec.
Examples:
- legacy VGA IO and memory (no corresponding BARs);
- base/limit registers of P2P bridge;
- PMU and SMBus registers (sort of normal BARs, but hidden elsewhere
in the config space);
- IDE legacy mode registers;
- IO-APIC registers (typically sort of read-only BAR).
For all of these address ranges our current BAR probe is effectively
a no-op, but disable/re-enable clearly isn't.
There are two other solutions: one is to disable decode selectively,
only on devices or systems where it's necessary and known to be safe.
I've posted a patch which introduces "disable_while_probe" pci_dev field
for that purpose.
Another one is to delay mmconfig probe until after the PCI probe is done,
as Matthew suggested, and Robert confirmed that it's feasible.
Ivan.
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