PCI: Tune secondary bus reset timing

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The PCI spec indicates that with stable power, reset needs to be
asserted for a minimum of 1ms (Trst).  We should be able to assume
stable power for a Hot Reset, but we add another millisecond as
a fudge factor to make sure the reset is seen on the bus for at least
a full 1ms.

After reset is de-asserted we must wait for devices to complete
initialization.  The specs refer to this as "recovery time" (Trhfa).
For PCI this is 2^25 clock cycles or 2^26 for PCI-X.  For minimum
bus speeds, both of those come to 1s.  PCIe "softens" this
requirement with the Configuration Request Retry Status (CRS)
completion status.  Theoretically we could use CRS to shorten the
wait time.  We don't make use of that here, using a fixed 1s delay
to allow devices to re-initialize.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

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Alex Williamson 2013-08-08 14:10:13 -06:00 • committed by Bjorn Helgaas

parent a6cbaadea0

commit de0c548c33

1 changed files with 14 additions and 2 deletions

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drivers/pci/pci.c

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