Re: [PATCH] Hamachi not doing pci_enable before reading resources

From: Jeff Garzik (
Date: Wed Feb 07 2001 - 15:05:56 EST

"Richard B. Johnson" wrote:
> A PCI device does not and should not be enabled to probe for resources!

Some PCI devices do not -have- resources until pci_enable_device() is
called, hence the rule.

> It is only devices that have BIOS that require the device to be enabled
> for memory I/O prior to downloading the BIOS into RAM. The BARs are
> read/writable (and are required to be), even when the Mem/I/O bits
> in the cmd/status register are clear.
> This is a required condition! You certainly don't want to write all
> ones to a decode (to find the resource length) of a live, on-line chip!
> If the chip hickups (think network chips connected to networks, on a
> warm-boot), you will trash lots of stuff in memory.

When writing 0xFFFFFFFF to a BAR to find its length, you must disable IO
and MEM decoding. This is a ideally what we should be doing anyway..
But you can re-enabling decoding once region size detection is
complete. AND. Region sizing only occurs once, and the value is cached
in dev->resource[], so it should not be occurring all over again, even
if pci_enable_device() is called.

> It looks as though you are "fixing" drivers that are not broken and,
> in fact, are trying to do the right thing. Maybe the PCI code in the
> kernel is preventing access to resources unless the device has been
> enabled??? If so, it's broken and should be fixed, instead of all
> the drivers.

wrong, you just missed this new "rule"...


Jeff Garzik       | "You see, in this world there's two kinds of
Building 1024     |  people, my friend: Those with loaded guns
MandrakeSoft      |  and those who dig. You dig."  --Blondie
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