On 1/8/2024 7:49 PM, Lukas Wunner wrote:
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On Thu, Jan 04, 2024 at 08:01:06PM +0530, Vidya Sagar wrote:
On 8/1/2023 1:29 AM, Lukas Wunner wrote:
As an alternative to disabling ACS, have you explored masking ACS
Violations (PCI_ERR_UNC_ACSV) upon de-enumeration of a device and
unmasking them after assignment of a bus number?
I explored this option and it seemed to work as expected. But, the issue
is that this works only if the AER registers are owned by the OS. If the
AER registers are owned by the firmware (i.e. Firmware-First approach of
handling the errors), OS is not supposed to access the AER registers and
there is no indication from the OS to the firmware as to when the
enumeration is completed and time is apt to unmask the ACSViolation
errors in the AER's Uncorrectable Error Mask register.
Any thoughts on accommodating the Firmware-First approach also?
Are you actually using firmware-controlled AER or is it a theoretical
question?
Yes. We indeed have a system with Firmware-Controlled AER.
PCI Firmware Spec r3.3 sec 4.6.12 talks about a _DSM to disable DPC
on surprise-hotplug-capable ports. Maybe that would be an option?
It looks like this _DSM is totally dependent on the port having SFI
capability implemented and unfortunately our system doesn't have
SFI implemented.
BTW what happens if the system resumes from sleep and a device in
a hotplug-capable port doesn't have a bus number configured yet
(because it's been powered off and is now in D0uninitialized state)?
Theoretically the answer seems to be yes, but, since the platform we
have is a server platform, there is no support for sleep and resume on
this platform and hence can't really confirm this behavior though.
Could the ACS Violations then occur as well? Do we have to mask
ACS Violations *generally* on Root Ports and Downstream Ports when
going to system sleep and unmask them after setting a bus number
in the attached device on resume? And I suppose that would not
only be necessary for hotplug ports?
Again, how to do that in a system where AER is not handled natively in
the OS? AFAIU, there is no mechanism for the OS to inform about the time
it updates the bus number.
Thanks,
Lukas
