On 6/20/2021 2:38 AM, Lukas Wunner wrote:
On Wed, Jun 16, 2021 at 05:19:45PM -0500, Bjorn Helgaas wrote:
On Sat, May 01, 2021 at 10:29:00AM +0200, Lukas Wunner wrote:
Downstream Port Containment (PCIe Base Spec, sec. 6.2.10) disables the
link upon an error and attempts to re-enable it when instructed by the
DPC driver.
A slot which is both DPC- and hotplug-capable is currently brought down
by pciehp once DPC is triggered (due to the link change) and brought up
on successful recovery. That's undesirable, the slot should remain up
so that the hotplugged device remains bound to its driver.
I think the slot being "brought down" means slot power is turned off,
right?
I reworded it along those lines and applied this to pci/hotplug for
v5.14, thanks!
Thanks, the reworded commit message LGTM and is more readable.
"Being brought down" is just a colloquial term for pciehp_disable_slot(),
i.e. unbinding and removal of the pci_dev's below the hotplug port,
removing slot power, turning off the power LED and setting the slot's
state to OFF_STATE.
Indeed, turning off slot power concurrently to DPC recovery is wrong
and likely the biggest contributor to the problems seen.
Another issue is that after bringing down the slot due to the Link Change
event, pciehp will notice that Presence Detect State is set and will try
to bring the slot up again, even though DPC recovery may not have completed
yet.
The commit should solve all those synchronization issues between pciehp
and DPC.
Thanks,
Lukas
Lukas--
I have a system that is failing to recover after an EDR event with (or
without...) this patch. It looks like the problem is similar to what
this patch is trying to fix, except that on my system, the hotplug port
is downstream of the root port that has DPC, so the "link down" event on
it is not being ignored. So the hotplug code disables the slot (which
contains an NVMe device on this system) while the nvme driver is trying
to use it, which results in a failed recovery and another EDR event, and
the kernel ends up with the DPC trigger status bit set in the root port,
so everything downstream is gone.
I added the hack below so the hotplug code will ignore the "link down"
events on the ports downstream of the root port during DPC recovery, and
it recovers no problem. (I'm not proposing this as a correct fix.)
Does this sound like a real issue, or am I possibly misunderstanding
something about how this should work?
Thanks
Stuart
diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index b576aa890c76..dfd983c3c5bf 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -119,8 +132,10 @@ static int report_slot_reset(struct pci_dev *dev,
void *data)
!dev->driver->err_handler->slot_reset)
goto out;
+ set_bit(PCI_DPC_RECOVERING, &dev->priv_flags);
err_handler = dev->driver->err_handler;
vote = err_handler->slot_reset(dev);
+ clear_bit(PCI_DPC_RECOVERING, &dev->priv_flags);
*result = merge_result(*result, vote);
out:
device_unlock(&dev->dev);
