On 2018-04-16 11:03, poza@xxxxxxxxxxxxxx wrote:
On 2018-04-16 08:47, Bjorn Helgaas wrote:
On Sat, Apr 14, 2018 at 11:53:17AM -0400, Sinan Kaya wrote:
You indicated that you want to unify the AER and DPC behavior. Let's
settle on what we want to do one more time. We have been going forth
and back on the direction.
My thinking is that as much as possible, similar events should be
handled similarly, whether the mechanism is AER, DPC, EEH, etc.
Ideally, drivers shouldn't have to be aware of which mechanism is in
use.
Error recovery includes conventional PCI as well, but right now I
think we're only concerned with PCIe. The following error types are
from PCIe r4.0, sec 6.2.2:
ERR_COR
Corrected by hardware with no software intervention. Software
involved for logging only.
Handled by AER via pci_error_handlers; DPC is never involved.
Link is unaffected.
ERR_NONFATAL
A transaction is unreliable but the link is fully functional.
If DPC is not supported, handled by AER via pci_error_handlers and
the link is unaffected.
If DPC supported, handled by DPC (because we set
PCI_EXP_DPC_CTL_EN_NONFATAL) via remove/re-enumerate.
ERR_FATAL
The link is unreliable.
If DPC is not supported, handled by AER via pci_error_handlers and
the link is reset.
If DPC supported, handled by DPC via remove/re-enumerate.
It doesn't seem right to me that we handle both ERR_NONFATAL and
ERR_FATAL events differently if we happen to have DPC support in a
switch.
Maybe we should consider triggering DPC only on ERR_FATAL? That would
keep DPC out of the ERR_NONFATAL cases.
For ERR_FATAL, maybe we should bite the bullet and use
remove/re-enumerate for AER as well as for DPC. That would be painful
for higher-level software, but if we're willing to accept that pain
for new systems that support DPC, maybe life would be better overall
if it worked the same way on systems without DPC?
Bjorn
This had crossed my mind when I first looked at the code.
DPC is getting triggered for both ERR_NONFATAL and ERR_FATAL case.
I thought the primary purpose of DPC to recover fatal errors, by
triggering HW recovery.
but what if some platform wants to handle both FATAL and NON_FATAL with
DPC ?
As you said AER FATAL cases and DPC FATAL cases should be handled
similarly.
e.g. remove/re-enumerate the devices.
while NON_FATAL case; only AER would come into picture.
if some platform would like to handle DPC NON_FATAL then it should
follow AER NON_FATAL path (where it does not do remove/re-enumerate)
And the case where hotplug is enabled, remove/re-enumerate more sense
in case of ERR_FATAL.
And the case where hotplug is disabled, only re-enumeration is
required. (no need to remove the devices)
but then do we need to handle this case specifically, what is the harm
in removing the devices in all the cases followed by re-enumerate ?
To Clarify the last line, what I meant here was, in case of ERR_FATAL we
can always remove/re-enumerate the devices irrespective of hotplug is
enabled or not.
and in case of ERR_NONFATAL, DPC will follow AER path (where it just
tries to recover)
although I am not very sure that how to handle ERR_NONFATAL case if
hotplug is enabled. Because as Keith suggested device might have been
changed run-time.
Regards,
Oza.
