Messages in this thread |  | | Date | Thu, 9 Nov 2000 21:37:41 +0100 (CET) | From | Gérard Roudier <> | Subject | Re: PCI-PCI bridges mess in 2.4.x |
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On Thu, 9 Nov 2000, Ivan Kokshaysky wrote:
Hmmm... The PCI spec. says that Limit registers define the top addresses _inclusive_.
The spec. does not seem to imagine that a Limit register lower than the corresponding Base register will ever exist anywhere, in my opinion. :-)
This let me think that trying to be clever here is probably a very bad idea. What is so catastrophic of having 1 to 4 bytes of addresses and no more being possibly in a forwardable range?
Gérard.
> 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); > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > Please read the FAQ at http://www.tux.org/lkml/ >
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