Re: [PATCH] PCI: Add quirk for Cavium Thunder-X2 PCIe erratum #173

[George Cherian <gcherian@caviumnetworks.com>]

Hi Bjorn,


On 02/22/2018 08:39 PM, Bjorn Helgaas wrote:
> On Thu, Feb 22, 2018 at 06:43:34PM +0530, George Cherian wrote:
>> On 02/22/2018 04:50 AM, Bjorn Helgaas wrote:
>>> On Wed, Feb 21, 2018 at 04:25:08PM +0530, George Cherian wrote:
>>>> On 02/21/2018 03:24 PM, Lukas Wunner wrote:
>>>>> On Wed, Feb 21, 2018 at 02:58:13PM +0530, George Cherian wrote:
>>>>>> I will explain the setup used
>>>>>> To the Cavium ThunderX RC the following PLX device is connected.
>>>>>> PLX Technology, Inc. PEX 8747 48-Lane, 5-Port PCI Express
>>>>>> Gen 3 (8.0 GT/s) Switch
>>>>>> There is no device connected downstream to the PLX switch.
>>>>>>
>>>>>> AFAIU the pcie_port driver probes PLX and enters autosuspend
>>>>>> after 100ms since pci_bridge_d3_possible() returns true.
>>>>>>
>>>>>> And later pci_sysfs_init() ends up doing a config access of
>>>>>> PLX which fails with a "synchronous external abort"
> 
>>>
>>> Thanks for the details!
>>>
>>> This one *should* be fixed by this patch:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/commit/?h=pci/virtualization&id=bf6c089ee2ac67eb22c0ff0ac9cc7f9ccd619d90
>>>
>>> Any chance you could try that out?
>>
>> I did try your patch and it works fine on the above failing setup.
> 
> Thanks for testing it!
> 
>>>> I have found another configuration where this fails.
>>>> Following is the configuration
>>>> 1) Connected a PCIe Intel i40 card under the root port.
>>>> 2) unbind the i40 driver and bind with vfio-pci driver.
>>>> 3) Run lspci in a loop. "lspci -s xx:xx.xx -vvv"
>>>>
>>>> I get the same synchronous external abort.
>>>> In this case the vfio-pci driver probe it moves the device (i40) to
>>>> D3hot provided disable_idle_d3 is not set. lspci tries to do
>>>> the config_access which fails with synchronous external abort when
>>>> the root port transitions to D3hot.
> 
> <snip>
>> the stack trace for this issue looks like this
>> [<ffff00000851bbfc>] pci_generic_config_read+0x5c/0xf0
>> [<ffff00000851c6e4>] pci_user_read_config_dword+0x84/0x110
>> [<ffff00000851cda8>] pci_vpd_read+0x100/0x208
>> [<ffff00000851bee8>] pci_read_vpd+0x50/0x68
>> [<ffff00000852d6c0>] read_vpd_attr+0x60/0x80
>> [<ffff00000833b224>] sysfs_kf_bin_read+0x6c/0xa8
>> [<ffff00000833a674>] kernfs_fop_read+0xa4/0x1c8
>> [<ffff0000082a6238>] __vfs_read+0x60/0x170
>> [<ffff0000082a63d4>] vfs_read+0x8c/0x148
>> [<ffff0000082a6c64>] SyS_pread64+0xbc/0xd8
>>
>> I have tried adding pci_config_pm_runtime_get/put pair inside
>> pci_vpd_read(), which I guess might be needed, in case the device goes
>> to D3cold. But having said that it didnt fix the problem in our platform.
> 
> Your original patch avoids this problem by setting PCI_DEV_FLAGS_NO_D3
> on the root port, so it seems like this must be somehow related to the
> root port's state.

This seems to be another issue and is not related to $SUBJECT.
Our Hardware team is internally looking into the same and will keep you 
posted of any further details.

Thanks for your time and suggestions.
> 
> I assume this VPD read is on the i40 device, right?  Since you're
> still seeing the problem even after calling
> pci_config_pm_runtime_get(), I assume the root port is still not in
> D0.  Can you add a little more instrumentation to read PCI_PM_CTRL and
> PCI_PM_PPB_EXTENSIONS for the root port and PCI_PM_CTRL for the i40
> device right after you call pci_config_pm_runtime_get()?
> 
> I don't see anything obviously different between the pci_read_config()
> path and the pci_vpd_read() path except for the
> pci_config_pm_runtime_get() call that you've already added.  I guess
> you could try using setpci instead of lspci to see if the failure only
> happens in the pci_vpd_read() path.  I assume that will be the case
> because lspci probably does config reads before it does the VPD read,
> and those initial config reads seemed to work OK.
> 
> The VPD path does do config writes in addition to config reads.  Maybe
> there's something special about writes, although I don't know what
> that would be.  You can tell I'm running out of ideas here :)
> 
> Bjorn
> 
-George