Ivan Passos wrote:
> Now, just out of curiosity: since the PCI allocation scheme makes sure
> that MMIO regions do not overlap, why is it necessary to request these
> regions to the OS?? For I/O regions, I understand, because an ISA device
> can try and probe an area where a PCI device is mapped. However, for MMIO
> regions, since most PCI devices are mapped above 1MB, ISA devices can't
> foul around with them. Is this mostly to protect PCI devices mapped below
> 1MB, or is it also for other things?!?!
Requesting MMIO regions protects against all sorts of cases, seen and
unseen. The core PCI code uses the resource system to allocate an
address space for new hotplugged device. Drivers mainly use the system
to protect against each other -- for more generic hardware, two drivers
might exist for the same hardware. The resource system prevents the
second driver from acquiring PCI MMIO resources registered by the first
driver. Or, there might be a driver bug which caused it to calculate an
incorrect base address. The resource system would prevent such a buggy
driver from obtaining resources already reserved to another.
Jeff
-- Jeff Garzik | Building 1024 | Yossarian lives. MandrakeSoft, Inc. |- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
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