[PATCH] PCI: Avoid leaving MASTER_ABORT disabled permanently when returning from...

[PATCH] PCI: Avoid leaving MASTER_ABORT disabled permanently when returning from pci_scan_bridge.

> On Mon, Feb 13, 2006 at 05:13:21PM -0800, David S. Miller wrote:
> >
> > In drivers/pci/probe.c:pci_scan_bridge(), if this is not the first
> > pass (pass != 0) we don't restore the PCI_BRIDGE_CONTROL_REGISTER and
> > thus leave PCI_BRIDGE_CTL_MASTER_ABORT off:
> >
> > int __devinit pci_scan_bridge(struct pci_bus *bus, struct pci_dev * dev, int max, int pass)
> > {
> >  ...
> > 	/* Disable MasterAbortMode during probing to avoid reporting
> > 	   of bus errors (in some architectures) */
> > 	pci_read_config_word(dev, PCI_BRIDGE_CONTROL, &bctl);
> > 	pci_write_config_word(dev, PCI_BRIDGE_CONTROL,
> > 			      bctl & ~PCI_BRIDGE_CTL_MASTER_ABORT);
> >  ...
> > 	if ((buses & 0xffff00) && !pcibios_assign_all_busses() && !is_cardbus) {
> > 		unsigned int cmax, busnr;
> > 		/*
> > 		 * Bus already configured by firmware, process it in the first
> > 		 * pass and just note the configuration.
> > 		 */
> > 		if (pass)
> > 			return max;
> >  ...
> > 	}
> >
> > 	pci_write_config_word(dev, PCI_BRIDGE_CONTROL, bctl);
> >  ...
> >
> > This doesn't seem intentional.

Agreed, looks like an accident.  The patch [1] originally came from Kip
Walker (Broadcom back then) between 2.6.0-test3 and 2.6.0-test4.  As I
recall it was supposed to fix an issue with with PCI aborts being
signalled by the PCI bridge of the Broadcom BCM1250 family of SOCs when
probing behind pci_scan_bridge.  It is undeseriable to disable
PCI_BRIDGE_CTL_MASTER_ABORT in pci_{read,write)_config_* and the
behaviour wasn't considered a bug in need of a workaround, so this was
put in probe.c.

I don't have an affected system at hand, so can't really test but I
propose something like the below patch.

[1] http://www.linux-mips.org/git?p=linux.git;a=commit;h=599457e0cb702a31a3247ea6a5d9c6c99c4cf195

[PCI] Avoid leaving MASTER_ABORT disabled permanently when returning from pci_scan_bridge.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>