Matthew, So, if I understand correctly, you are saying because we cannot guarantee the "flush" a config write even by doing a config read of the same register (because the PPB can re-order) we have to make sure we block or spin on the config write completion at the lowest level of the config write ? Thanks John Matthew Wilcox wrote:
On Wed, Nov 01, 2006 at 10:27:19AM -0600, John Partridge wrote:Sorry, but I find this change a bit puzzling. The problem is particular to the PPB on the HCA and not Altix.That's not true; it's more likely on Altix, but it's not unique. *any* PCI-PCI bridge can reorder pci config reads and writes. Apparently the normal PCI host bridge implementation avoids this problem by blocking until the completion comes back. If you put a quad-port tulip card into an Altix, you could experience the same problem (but it would be massively unlikely. You'd probably have to bring up three interfaces, saturate them with traffic, then bring up the fourth to see it. And even then it would be rare).I can't see anywhere that a PCI Config Writeis required to block until completion, it is the driver and the HCA ,not the Altix hardware that requires the Config Write to have completed before we leave mthca_reset()There's several places in the PCI midlayer that require the config write to have completed before we do a config read. The MWI code relies on this to see if the device supports MWI. If it gets out of order, we'll think that the device doesn't support MWI when it thinks it's been told to use MWI. Data corruption could result.Changing pci_write_config_xxx() will change the behavior for ALL drivers and the possibility of breaking something else. The fix was very low risk in mthca_reset(), changing the PCI code to fix this is much more onerous.I really don't think so. At worst you'll be changing the timing.
-- John Partridge Silicon Graphics Inc Tel: 651-683-3428 Vnet: 233-3428 E-Mail: johnip@xxxxxxx - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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