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

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Date:   Wed, 21 Feb 2018 16:25:08 +0530
From:   George Cherian <gcherian@...iumnetworks.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        bhelgaas@...gle.com, Jayachandran.Nair@...ium.com,
        Robert.Richter@...ium.com,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Huang Ying <ying.huang@...el.com>
Subject: Re: [PATCH] PCI: Add quirk for Cavium Thunder-X2 PCIe erratum #173

Hi Lukas,

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"
> 
> Then you're missing a pci_config_pm_runtime_get() in pci_sysfs_init() or
> further down in the call stack, rather than a quirk which just papers
> over the issue.

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.
> 
> Thanks,
> 
> Lukas
> 
Regards,
-George