Messages in this thread |  | | | Date | Mon, 6 Jan 2003 18:33:28 +0300 | | From | Ivan Kokshaysky <> | | Subject | Re: [patch 2.5] PCI: allow alternative methods for probing the BARs |
| |
On Sun, Jan 05, 2003 at 08:14:53PM -0800, Linus Torvalds wrote: > Can you do the same with a multi-pass thing? > > I really think the single-pass approach is broken, because it means that > we _cannot_ have a fixup for device that runs _before_ the fixup for the > bridge that bridges to the device. > > As such, the "PCI_FIXUP_EARLY" is not _nearly_ early enough, since it's > way too late for the actual problem that started this whole thread (ie in > order to turn off a bridge, we have to make sure that everything behind > the bridge is turned off _first_).
I totally agree, 2-phase approach is a right way to go. However, I've been confused by that "feature freeze" thing. ;-) This patch has zero impact on existing code - I thought it's a "feature" (and I still believe it's ok for 2.4). OTOH, I've actually tried to implement 2-phase probing _inside_ the pci_do_scan_bus, and that was ugly as hell. I believe the phase #2 must be a separate top-level function - something like pci_probe_resources (better naming?), but this assumes some changes to PCI code for every architecture and hotplug drivers.
> In other words, we really should be able to do all the bus number setup > _first_. That isn't dependent ont eh BAR's or anything else. The actual > _sizing_ of the bus is clearly somethign we cannot do early, but we can > (and should) enumerate the devices first in phase #1. > > Alternatively, we could even have a very limited phase #1 that only > enumerates _reachable_ devices (ie it doesn't even try to create bus > numbers, it only enumerates devices and buses that have already been set > up by the firmware, and ignores bridges that aren't set up yet). A pure > discovery phase, without any configuration at all.
I like the former. Even if we have to reassign the bus numbers, we won't affect anything but forwarding the PCI configuration cycles.
For now I'd start with following: phase #1. pci_do_scan_bus() - build the bus/device tree, read in dev/vendor IDs, header type and class code; call "PCI_FIXUP_EARLY" fixups. phase #2. pci_probe_resources(bus) - walk the bus tree again, probe the BARs, maybe call pci_read_bridge_bases for bridges; fill in the rest of PCI header; call "PCI_FIXUP_HEADER" fixups. (Also there are phases #3 and #4 - assign resources and assign unassigned resources, but it's another story)
Then, for example on alpha, we'll have
/* Scan all of the recorded PCI controllers. */ for (next_busno = 0, hose = hose_head; hose; hose = hose->next) { hose->first_busno = next_busno; hose->last_busno = 0xff; bus = pci_scan_bus(next_busno, alpha_mv.pci_ops, hose); hose->bus = bus; next_busno = hose->last_busno = bus->subordinate; + pci_probe_resources(bus); next_busno += 1; } Hmm, this looks good - now we can do early bus-specific fixups without introducing "pcibios_init_bus" thing (suggested by Grant and myself quite a while ago).
I'll try to code up all of this and do some basic testing on alpha and i386 in next few days.
Comments?
Ivan. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |