On Mon, Feb 13, 2006 at 09:17:00PM -0800, Greg KH wrote:
> Date: Mon, 13 Feb 2006 21:17:00 -0800
> From: Greg KH <[email protected]>
> To: "David S. Miller" <[email protected]>
> Cc: [email protected], [email protected],
> [email protected]
> Subject: Re: PCI probe leaves master abort disabled in PCI_BRIDGE_CONTROL
> Content-Type: text/plain; charset=us-ascii
>
> 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.
>
> No it doesn't. Ralf added that code, way back in 2.6.2-rc2, with a
> patch description of "[PATCH] PCI: fix probing for some mips systems"
>
> David, does this break some stuff on your boxes?
>
> Ralf, any thoughts? It was way back in January of 2004 that this change
> went in.
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.
Ralf
[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 <[email protected]>
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index adfad4f..6de7c59 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -456,7 +456,7 @@ int __devinit pci_scan_bridge(struct pci
* pass and just note the configuration.
*/
if (pass)
- return max;
+ goto out;
busnr = (buses >> 8) & 0xFF;
/*
@@ -466,12 +466,12 @@ int __devinit pci_scan_bridge(struct pci
if (pci_find_bus(pci_domain_nr(bus), busnr)) {
printk(KERN_INFO "PCI: Bus %04x:%02x already known\n",
pci_domain_nr(bus), busnr);
- return max;
+ goto out;
}
child = pci_add_new_bus(bus, dev, busnr);
if (!child)
- return max;
+ goto out;
child->primary = buses & 0xFF;
child->subordinate = (buses >> 16) & 0xFF;
child->bridge_ctl = bctl;
@@ -496,7 +496,7 @@ int __devinit pci_scan_bridge(struct pci
bus ranges. */
pci_write_config_dword(dev, PCI_PRIMARY_BUS,
buses & ~0xffffff);
- return max;
+ goto out;
}
/* Clear errors */
@@ -505,7 +505,7 @@ int __devinit pci_scan_bridge(struct pci
/* Prevent assigning a bus number that already exists.
* This can happen when a bridge is hot-plugged */
if (pci_find_bus(pci_domain_nr(bus), max+1))
- return max;
+ goto out;
child = pci_add_new_bus(bus, dev, ++max);
buses = (buses & 0xff000000)
| ((unsigned int)(child->primary) << 0)
@@ -576,8 +576,6 @@ int __devinit pci_scan_bridge(struct pci
pci_write_config_byte(dev, PCI_SUBORDINATE_BUS, max);
}
- pci_write_config_word(dev, PCI_BRIDGE_CONTROL, bctl);
-
sprintf(child->name, (is_cardbus ? "PCI CardBus #%02x" : "PCI Bus #%02x"), child->number);
while (bus->parent) {
@@ -596,6 +594,9 @@ int __devinit pci_scan_bridge(struct pci
bus = bus->parent;
}
+out:
+ pci_write_config_word(dev, PCI_BRIDGE_CONTROL, bctl);
+
return max;
}
-
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