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SubjectRe: PCI-PCI bridges mess in 2.4.x
On Wed, Nov 08, 2000 at 03:48:11PM -0800, Richard Henderson wrote:
> Whee! We're back in Bootsville.

Cool!
Meanwhile this base/limit stuff got confirmation :-)
Here is a patch against bridges-2.4.0t11-rth.

Ivan.

--- 2.4.0t11p1/drivers/pci/setup-bus.c Wed Nov 8 19:44:42 2000
+++ linux/drivers/pci/setup-bus.c Thu Nov 9 15:11:01 2000
@@ -88,14 +88,14 @@ pbus_assign_resources_sorted(struct pci_
ranges->io_end += io_reserved;
ranges->mem_end += mem_reserved;

- /* ??? How to turn off a bus from responding to, say, I/O at
- all if there are no I/O ports behind the bus? Turning off
- PCI_COMMAND_IO doesn't seem to do the job. So we must
- allow for at least one unit. */
- if (ranges->io_end == ranges->io_start)
- ranges->io_end += 1;
- if (ranges->mem_end == ranges->mem_start)
- ranges->mem_end += 1;
+ /* Interesting case is when, say, io_end == io_start, i.e.
+ there is no I/O behind the bridge at all. We initialize
+ the bridge with base=io_start and limit=io_end-1, so
+ in this case we'll have base > limit. According to
+ the `PCI-to-PCI Bridge Architecture Specification', this
+ means that the bridge will not forward any I/O transactions
+ from the primary bus to the secondary bus and will forward
+ all I/O transactions upstream. Exactly what we want. */

ranges->io_end = ROUND_UP(ranges->io_end, 4*1024);
ranges->mem_end = ROUND_UP(ranges->mem_end, 1024*1024);
-
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