On 02.02.2018 14:56, Mika Westerberg wrote:
On Fri, Feb 02, 2018 at 02:38:34PM +0100, Stefan Roese wrote:
Hi Mika,
sorry for the late reply.
On 30.01.2018 11:28, Mika Westerberg wrote:
On Tue, Jan 30, 2018 at 09:41:21AM +0100, Stefan Roese wrote:
Hotplugging of some PCIe devices on our platform sometimes leads to a
bounce of link-up and link-down events, resulting in problems in the
corresponding PCI drivers.
Here an example of such a hotplug event bounce for a AHCI PCIe card:
...
pciehp 0000:00:1c.1:pcie004: Slot(1): Card present
pciehp 0000:00:1c.1:pcie004: Slot(1): Link Up
pciehp 0000:00:1c.1:pcie004: Slot(1): Link Up event ignored; already powering on
pciehp 0000:00:1c.1:pcie004: Slot(1): Link Down
pciehp 0000:00:1c.1:pcie004: Slot(1): Card present
pciehp 0000:00:1c.1:pcie004: Slot(1): Link Up
It would be good to find out why this happens in the first place.
Perhaps there is some environmental interference or something causing
this?
I'm seeing these link bounces in the following environments:
a) Using a BayTrail SoC and hotplugging a standard Desktop PCIe SATA /
AHCI Controller (Marvell chip)
b) Hotplugging (booting via SPI) an Altera / Intel FPGA which is connected
via PCIe to a PCIe switch
In both cases, this link bouncing happens infrequently, approx. once out
of 5 - 10 tries.
Out of curiosity, has nobody else ever experienced such "link bouncing"
with PCIe cards / devices getting hot-plugged?
I've seen it with some Thunderbolt devices from time to time.
I think it is entirely possible in real world that the link goes down
briefly for example because of some external interference so we should
make sure we can handle that properly.
pci 0000:02:00.0: [1b4b:9215] type 00 class 0x010601
pci 0000:02:00.0: reg 0x10: [io 0x8000-0x8007]
...
ata3: SATA max UDMA/133 abar m2048@0x80910000 port 0x80910100 irq 100
ata4: SATA max UDMA/133 abar m2048@0x80910000 port 0x80910180 irq 100
ata5: SATA max UDMA/133 abar m2048@0x80910000 port 0x80910200 irq 100
ata6: SATA max UDMA/133 abar m2048@0x80910000 port 0x80910280 irq 100
pciehp 0000:00:1c.1:pcie004: Slot(1): Link Up event ignored; already powering on
ahci 0000:02:00.0: PME# disabled
ata3: SATA link down (SStatus 0 SControl 300)
ata5: SATA link down (SStatus 0 SControl 300)
ata4: SATA link down (SStatus 0 SControl 300)
WARNING: CPU: 2 PID: 1162 at drivers/ata/libata-core.c:6620 ata_host_detach+0x125/0x130
I think the AHCI driver should be fixed to cope with this.
Yes, this can be discussed. But still the root-cause should be fixed,
IMHO. Either in our environment (HW issue?) or by adding this de-bouncing
feature.
ata6: SATA link down (SStatus 0 SControl 300)
Modules linked in:
CPU: 2 PID: 1162 Comm: kworker/u8:5 Not tainted 4.15.0+ #26
Hardware name: congatec conga-qeval20-qa3-e3845/conga-qeval20-qa3-e3845, BIOS 2018.01-00033-g0125f37185-dirty 01/18/2018
Workqueue: pciehp-1 pciehp_power_thread
...
This patch now adds the 'pciehp_debounce_time' module parameter, which
can be used to drop all events for the specified time (in milliseconds)
after a link-up event occurred. A value of ~100ms works fine in my tests
to debounce all the link-up / link-down events in my tests.
This sounds a bit "hackish". I would rather make sure we can handle
situations like this properly without passing additional parameters.
I'm open for other / better ideas on how to solve this situation, we
are seeing on our systems.
Well, I would start by fixing drivers that can't cope with surprise link
down (e.g disapearing PCI device, or suddenly reading 0xffffffff from
register).
I've already sent a patch regarding a libata problem while unplugging
an AHCI controller:
https://www.spinics.net/lists/linux-ide/msg55038.html
BTW, have you checked whether presence detect actually toggles similarly
or is it only triggered when the link is fully up? Since currently we
prioritize link up/down higher than presence detect but it may be that
we should do the opposite.
As seen in the log sent in my previous mail, presence detect also
toggles. Here again:
[ 41.260667] pciehp 0000:00:1c.1:pcie004: Slot(1): Card present
[ 41.260731] pciehp 0000:00:1c.1:pcie004: Slot(1): Link Up
[ 41.290650] pciehp 0000:00:1c.1:pcie004: Slot(1): Link Down
[ 41.295837] pciehp 0000:00:1c.1:pcie004: Slot(1): Card present
[ 41.320664] pciehp 0000:00:1c.1:pcie004: Slot(1): Card not present
[ 41.330042] pciehp 0000:00:1c.1:pcie004: Slot(1): Card present
[ 41.330110] pciehp 0000:00:1c.1:pcie004: Slot(1): Link Up
[ 41.375950] pci 0000:02:00.0: [1b4b:9215] type 00 class 0x010601
...
Even though I'm wondering, why we are seeing 3 times "Card present"
and only one time "Card not present". I would expect to see 2
"Card present" messages here. This does not seem to be balanced
correctly.
Thanks,
Stefan
