Re: [PATCH] PCI fixes for 2.6.9

[Greg KH]

ChangeSet 1.1997.37.57, 2004/10/06 13:53:18-07:00, johnrose@xxxxxxxxxxxxxx

[PATCH] PCI Hotplug: RPA DLPAR - remove error check

Here's a really long explanation for a really short patch! :)

As an unfortunate side effect of runtime addition/removal of PCI Host Bridges,
the RPA DLPAR driver can no longer depend on the success of ioremap_explicit()
(and therefore remap_page_range()) for the case of DLPAR adding an I/O Slot.

Without addressing this, an attempt to add the first child slot of a newly
added PHB will fail when __ioremap_explicit() determines the mappings for that
range to already exist.

For a little context, __ioremap_explicit() creates mappings for the range of a
newly added slot.  Here's why these calls will be expected to fail in some
cases.  Keep in mind that at boot-time, the PPC64 kernel calls ioremap() for
the entire range spanned by each PHB.  Consider the following scenarios of
DLPAR-adding an I/O slot.

1) Just after boot, one removes an I/O slot.  At this point the range
   associated with the parent PHB is fragmented, and the child range for the
   slot in question is iounmap()'ed.  One then re-adds the slot, at which point
   remap_page_range()/ioremap_explicit() restores the mappings that were
   previously removed.

2) One adds a new PHB, at which point the ppc64-specific addition ioremaps the
   entire PHB range.  One then performs a DLPAR-add of a child slot of that
   PHB.  At this point, mappings already exist for the range of the slot to
   be added.  So remap_page_range()/ioremap_explicit() will fail at this point.

The problem is, there's not a good way to distinguish between cases 1 and 2
from the perspective of the DLPAR driver.  Because of that, I believe the
correct solution to be:

- Removal of relevant error prints from iounmap_explicit(), which is only used
  for DLPAR.
- Removal of error code checks from the RPA driver


Signed-off-by: John Rose <johnrose@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <greg@xxxxxxxxx>


 drivers/pci/hotplug/rpadlpar_core.c |    8 ++------
 1 files changed, 2 insertions(+), 6 deletions(-)


diff -Nru a/drivers/pci/hotplug/rpadlpar_core.c b/drivers/pci/hotplug/rpadlpar_core.c
--- a/drivers/pci/hotplug/rpadlpar_core.c	2004-10-19 15:22:29 -07:00
+++ b/drivers/pci/hotplug/rpadlpar_core.c	2004-10-19 15:22:29 -07:00
@@ -158,12 +158,8 @@
 
 	dn->bussubno = child->number;
 
-	/* ioremap() for child bus */
-	if (remap_bus_range(child)) {
-		printk(KERN_ERR "%s: could not ioremap() child bus\n",
-			__FUNCTION__);
-		return 1;
-	}
+	/* ioremap() for child bus, which may or may not succeed */
+	remap_bus_range(child);
 
 	return 0;
 }

-
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