From: "Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@linux.intel.com>
To: Lukas Wunner <lukas@wunner.de>,
Bjorn Helgaas <helgaas@kernel.org>,
Dan Williams <dan.j.williams@intel.com>
Cc: Ethan Zhao <haifeng.zhao@intel.com>,
Sinan Kaya <okaya@kernel.org>, Ashok Raj <ashok.raj@intel.com>,
Keith Busch <kbusch@kernel.org>,
linux-pci@vger.kernel.org, Russell Currey <ruscur@russell.cc>,
Oliver O'Halloran <oohall@gmail.com>,
Stuart Hayes <stuart.w.hayes@gmail.com>,
Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: Re: [PATCH] PCI: pciehp: Ignore Link Down/Up caused by DPC
Date: Tue, 27 Apr 2021 17:39:43 -0700 [thread overview]
Message-ID: <c7a09e8d-d2a9-02c9-8ac1-224147bd7827@linux.intel.com> (raw)
In-Reply-To: <13bbd4f9-dff4-be79-d80a-342399961939@linux.intel.com>
Hi Bjorn,
On 3/30/21 1:53 PM, Kuppuswamy, Sathyanarayanan 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. DPC notifies
>> the driver of the error and of successful recovery in pcie_do_recovery()
>> and the driver may then restore the device to working state.
>>
>> Moreover, Sinan points out that turning off slot power by pciehp may
>> foil recovery by DPC: Power off/on is a cold reset concurrently to
>> DPC's warm reset. Sathyanarayanan reports extended delays or failure
>> in link retraining by DPC if pciehp brings down the slot.
>>
>> Fix by detecting whether a Link Down event is caused by DPC and awaiting
>> recovery if so. On successful recovery, ignore both the Link Down and
>> the subsequent Link Up event.
>>
>> Afterwards, check whether the link is down to detect surprise-removal or
>> another DPC event immediately after DPC recovery. Ensure that the
>> corresponding DLLSC event is not ignored by synthesizing it and
>> invoking irq_wake_thread() to trigger a re-run of pciehp_ist().
>>
>> The IRQ threads of the hotplug and DPC drivers, pciehp_ist() and
>> dpc_handler(), race against each other. If pciehp is faster than DPC,
>> it will wait until DPC recovery completes.
>>
>> Recovery consists of two steps: The first step (waiting for link
>> disablement) is recognizable by pciehp through a set DPC Trigger Status
>> bit. The second step (waiting for link retraining) is recognizable
>> through a newly introduced PCI_DPC_RECOVERING flag.
>>
>> If DPC is faster than pciehp, neither of the two flags will be set and
>> pciehp may glean the recovery status from the new PCI_DPC_RECOVERED flag.
>> The flag is zero if DPC didn't occur at all, hence DLLSC events are not
>> ignored by default.
>>
>> This commit draws inspiration from previous attempts to synchronize DPC
>> with pciehp:
>>
>> By Sinan Kaya, August 2018:
>> https://lore.kernel.org/linux-pci/20180818065126.77912-1-okaya@kernel.org/
>>
>> By Ethan Zhao, October 2020:
>> https://lore.kernel.org/linux-pci/20201007113158.48933-1-haifeng.zhao@intel.com/
>>
>> By Sathyanarayanan Kuppuswamy, March 2021:
>> https://lore.kernel.org/linux-pci/59cb30f5e5ac6d65427ceaadf1012b2ba8dbf66c.1615606143.git.sathyanarayanan.kuppuswamy@linux.intel.com/
>>
> Looks good to me. This patch fixes the reported issue in our environment.
>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> Tested-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Any update on this patch? is this queued for merge? One of our customers is looking
for this fix. So wondering about the status.
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer
next prev parent reply other threads:[~2021-04-28 0:39 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-28 8:52 [PATCH] PCI: pciehp: Ignore Link Down/Up caused by DPC Lukas Wunner
2021-03-30 20:53 ` Kuppuswamy, Sathyanarayanan
2021-04-28 0:39 ` Kuppuswamy, Sathyanarayanan [this message]
2021-04-28 1:42 ` Zhao, Haifeng
2021-04-28 10:08 ` Yicong Yang
2021-04-28 14:40 ` Lukas Wunner
2021-04-29 11:29 ` Yicong Yang
2021-04-29 12:40 ` Zhao, Haifeng
2021-04-29 19:42 ` Lukas Wunner
2021-04-30 8:47 ` Yicong Yang
2021-04-30 12:15 ` Lukas Wunner
2021-04-29 19:36 ` Keith Busch
2021-04-29 20:16 ` Lukas Wunner
2021-04-29 21:16 ` Keith Busch
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