On 06/30/2018 04:31 PM, Bjorn Helgaas wrote:
[+cc Borislav, linux-acpi, since this involves APEI/HEST]
Borislav is not the relevant maintainer here, since we're not contingent
on APEI handling. I think Keith has a lot more experience with this part
of the kernel.
On Tue, Jun 19, 2018 at 02:58:20PM -0500, Alexandru Gagniuc wrote:
According to the documentation, "pcie_ports=native", linux should use
native AER and DPC services. While that is true for the _OSC method
parsing, this is not the only place that is checked. Should the HEST
table list PCIe ports as firmware-first, linux will not use native
services.
Nothing in ACPI-land looks at pcie_ports_native. How should ACPI
things work in the "pcie_ports=native" case? I guess we still have to
expect to receive error records from the firmware, because it may
certainly send us non-PCI errors (machine checks, etc) and maybe even
some PCI errors (even if the Linux AER driver claims AER interrupts,
we don't know what notification mechanisms the firmware may be using).
I think ACPI land shouldn't care about this. We care about it from the
PCIe stand point at the interface with ACPI. FW might see a delta in the
sense that we request control of some features via _OSC, which we
otherwise would not do without pcie_ports=native.
I guess best-case, we'll get ACPI error records for all non-PCI
things, and the Linux AER driver will see all the AER errors.
It might affect FW's ability to catch errors, but that's dependent on
the root port implementation.
Worst-case, I don't really know what to expect. Duplicate reporting
of AER errors via firmware and Linux AER driver? Some kind of
confusion about who acknowledges and clears them?
Once user enters pcie_ports=native, all bets are off: you broke the
contract you have with the FW -- whether or not you have this patch.
Out of curiosity, what is your use case for "pcie_ports=native"?
Presumably there's something that works better when using it, and
things work even *better* with this patch?
Corectness. It bothers me that actual behavior does not match the
documentation:
native Use native PCIe services associated with PCIe ports
unconditionally.
I know people do use it, because I often see it mentioned in forums
and bug reports, but I really don't expect it to work very well
because we're ignoring the usage model the firmware is designed
around. My unproven suspicion is that most uses are in the black
magic category of "there's a bug here, and we don't know how to fix
it, but pcie_ports=native makes it work better".
There exist cases that firmware didn't consider. I would not call them
"firmware bugs", but there are cases where the user understands the
platform better than firmware.
Example: on certain PCIe switches, a hardware PCIe error may bring the
switch downstream ports into a state where they stop notifying hotplug
events. Depending on the platform, firmware may or may not fix this
condition, but "pcie_ports=native" enables DPC. DPC contains the error
without the switch downstream port entering the weird error state in the
first place.
All bets are off at this point.
Obviously I would much rather find and fix those bugs so people
wouldn't have to stumble over the problem in the first place.
Using native services when firmware asks us not to is a crapshoot every
time. I don't condone the use of this feature, but if we do get a
pcie_ports=native request, we should at least honor it.
This happens because aer_acpi_firmware_first() doesn't take
'pcie_ports' into account. This is wrong. DPC uses the same logic when
it decides whether to load or not, so fixing this also fixes DPC not
loading.
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@xxxxxxxxx>
---
drivers/pci/pcie/aer.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
Changes since v1:
- Re-tested with latest and greatest (v4.18-rc1) -- works great
diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
index a2e88386af28..98ced0f7c850 100644
--- a/drivers/pci/pcie/aer.c
+++ b/drivers/pci/pcie/aer.c
@@ -291,7 +291,7 @@ static void aer_set_firmware_first(struct pci_dev *pci_dev)
rc = apei_hest_parse(aer_hest_parse, &info);
- if (rc)
+ if (rc || pcie_ports_native)
pci_dev->__aer_firmware_first = 0;
else
pci_dev->__aer_firmware_first = info.firmware_first;
@@ -327,6 +327,9 @@ bool aer_acpi_firmware_first(void)
apei_hest_parse(aer_hest_parse, &info);
aer_firmware_first = info.firmware_first;
parsed = true;
+ if (pcie_ports_native)
+ aer_firmware_first = 0;
+
}
return aer_firmware_first;
}
--
2.14.3
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