On 28 Jul 2020, at 10:02, Jonathan Cameron wrote:
On Tue, 28 Jul 2020 09:14:11 -0700
Sean V Kelley <sean.v.kelley@xxxxxxxxx> wrote:
On 28 Jul 2020, at 6:27, Zhuo, Qiuxu wrote:
From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Sent: Monday, July 27, 2020 7:17 PM
To: Kelley, Sean V <sean.v.kelley@xxxxxxxxx>
Cc: bhelgaas@xxxxxxxxxx; rjw@xxxxxxxxxxxxx; ashok.raj@xxxxxxxxxx;
Luck,
Tony <tony.luck@xxxxxxxxx>;
sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx;
linux-pci@xxxxxxxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx; Zhuo, Qiuxu <qiuxu.zhuo@xxxxxxxxx>
Subject: Re: [RFC PATCH 5/9] PCI/AER: Apply function level reset to
RCiEP
on fatal error
On Fri, 24 Jul 2020 10:22:19 -0700
Sean V Kelley <sean.v.kelley@xxxxxxxxx> wrote:
From: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>
Attempt to do function level reset for an RCiEP associated with an
RCEC device on fatal error.
I'd like to understand more on your reasoning for flr here.
Is it simply that it is all we can do, or is there some basis in a
spec
somewhere?
Yes. Though there isn't the link reset for the RCiEP here, I think
we
should still be able to reset the RCiEP via FLR on fatal error, if
the
RCiEP supports FLR.
-Qiuxu
Also see PCIe 5.0-1, Sec. 6.6.2 Function Level Reset (FLR)
Implementation of FLR is optional (not required), but is strongly
recommended. For an example use case consider CXL. Function 0 DVSEC
instances control for the CXL functionality of the entire CXL device.
FLR may succeed in recovering from CXL.io domain errors.
That feels a little bit of a weak argument in favour. PCI spec lists
examples
of use only for FLR and I can't see this matching any of them, but
then they
are only examples, so we could argue it doesn't exclude this use. It's
not
allowed to affect the link state, but I guess it 'might' recover from
some
other type of error?
I'd have read the statement in the CXL spec you are referring to as
matching
with the first example in the PCIe spec which is about recovering from
software errors. For example, unexpected VM tear down.
From my perspective, it can add value as the point is to address device
functions and their associated software states. As the section in the
spec goes on to state:
“The FLR mechanism enables software to quiesce and reset Endpoint
hardware with Function-level granularity. Three example usage models
illustrate the benefits of this feature:…”
Later changes in CXL 2.0 Section 9.8 (as of 0.9 draft) further look to
extend FLR with an eFLR or now referred to as CXL Reset.
“All Functions in a CXL 2.0 (Single Logical Device) SLD that
participate in CXL.cache or CXL.mem are required to support either FLR
or CXL Reset. MLDs (Multiple Logical Devices), on the other hand, are
required to support CXL Reset.”
In my mind the question is whether this change is too limited in scope
with this patch series (RCiEP) and whether FLR should be considered in a
broader, i.e., EP, as a ‘hammer’ so to speak.
Thanks,
Sean
@Bjorn / All. What's your view on using FLR as a reset to do when you
don't
have any other hammers to use?
Personally I don't have a particular problem with this, it just
doesn't fit
with my mental model of what FLR is for (which may well need adjusting
:)
Jonathan
Thanks,
Sean
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>
---
drivers/pci/pcie/err.c | 31 ++++++++++++++++++++++---------
1 file changed, 22 insertions(+), 9 deletions(-)
diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c index
044df004f20b..9b3ec94bdf1d 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -170,6 +170,17 @@ static void pci_walk_dev_affected(struct
pci_dev *dev, int (*cb)(struct pci_dev
}
}
+static enum pci_channel_state flr_on_rciep(struct pci_dev *dev) {
+if (!pcie_has_flr(dev))
+return PCI_ERS_RESULT_NONE;
+
+if (pcie_flr(dev))
+return PCI_ERS_RESULT_DISCONNECT;
+
+return PCI_ERS_RESULT_RECOVERED;
+}
+
pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
enum pci_channel_state state,
pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
@@ -191,15
+202,17 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
if (state == pci_channel_io_frozen) {
pci_walk_dev_affected(dev, report_frozen_detected,
&status);
if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
-pci_warn(dev, "link reset not possible for RCiEP\n");
-status = PCI_ERS_RESULT_NONE;
-goto failed;
-}
-
-status = reset_link(dev);
-if (status != PCI_ERS_RESULT_RECOVERED) {
-pci_warn(dev, "link reset failed\n");
-goto failed;
+status = flr_on_rciep(dev);
+if (status != PCI_ERS_RESULT_RECOVERED) {
+pci_warn(dev, "function level reset failed\n");
+goto failed;
+}
+} else {
+status = reset_link(dev);
+if (status != PCI_ERS_RESULT_RECOVERED) {
+pci_warn(dev, "link reset failed\n");
+goto failed;
+}
}
} else {
pci_walk_dev_affected(dev, report_normal_detected,
&status);
