On 4/17/2018 1:19 PM, Bjorn Helgaas wrote:
On Tue, Apr 17, 2018 at 03:56:13PM +0000, Marciniszyn, Mike wrote:
Btw, why is the driver configuring the PCIe link speed? Isn't this
something we should be handling in the PCI core?
The device comes out of reset at the 5GT/s speed. The driver
downloads device firmware, programs PCIe registers, and co-ordinates
the transition to 8GT/s.
This recipe is device specific and is therefore implemented in the
hfi1 driver built on top of PCI core functions and macros.
Do you think this behavior conforms to the spec, or is this a
workaround for a hardware erratum?
Can't speculate as to why, but this is just the way this hardware works.
I don't think it's feasible to have every driver deal with this level
of PCIe detail. Do you have to do something similar in the Windows
driver?
No Windows driver.
Is there something we can do in the PCI core to do the
reconfiguration? If you can't go to 8GT/s before doing some
device-specific initialization, could the driver do that setup and
then use a generic PCI core interface to reconfigure the link?
Or maybe if the driver finds the device at 5GT/s, it could download
the firmware and reset the device. Would the device then negotiate at
8GT/s?
Yes. In fact this is what we should be doing. We use the SBR to trigger
renegotiation of the link to 8GT/s.
-Denny
