On Tue, 29 Jul 2014, Alex Williamson wrote:
On Tue, 2014-07-29 at 10:30 -0600, Keith Busch wrote:
On Tue, 29 Jul 2014, Alex Williamson wrote:
On Tue, 2014-07-29 at 16:17 +0800, Yijing Wang wrote:
Currently we don't update device's mps value when doing
pci device hot-add. The hot-added device's mps will be set
to default value (128B). But the upstream port device's mps
may be larger than 128B which was set by firmware during
system bootup. In this case the new added device may not
work normally.
Apologies if we rehash some previously discussed topics while I try to
cover for Bjorn while he's out. By "normally", do you mean "optimally"?
The device should be functional with a lower mps setting, right?
You'd think so, but some platforms don't work. A pci-e trace showed
TLPs exceeding MPS when parent device at 256B and the end device left
at 128B. Even if that's a platform bug, I think we still want it to work.
But if it's a platform bug for a non-compliant device, should it be
handled as a quirk rather than standard configuration? Thanks,
I'm not even sure it is a platform bug, but that was just a guess. The
way the devices are configured, it appears they behave inline with the
spec (from table 7-13):
"
Max_Payload_size -- This field sets maximum TLP payload size for the
Function. As a Receiver, the Function must handle TLPs as large as the set
value. As a Transmitter, the Function must not generate TLPs exceeding the
set value.
"
It sounds like it allows a transmitter to generate a TLP that the receiver
can't handle, but I don't know if that was the intent. :)
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