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From: "Zhao, Haifeng" <haifeng.zhao@intel.com>
To: "Kuppuswamy,
	Sathyanarayanan"  <sathyanarayanan.kuppuswamy@linux.intel.com>,
	Lukas Wunner <lukas@wunner.de>,
	Bjorn Helgaas <helgaas@kernel.org>,
	"Williams, Dan J" <dan.j.williams@intel.com>
Cc: Sinan Kaya <okaya@kernel.org>, "Raj, Ashok" <ashok.raj@intel.com>,
	"Keith Busch" <kbusch@kernel.org>,
	"linux-pci@vger.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: Wed, 28 Apr 2021 01:42:12 +0000	[thread overview]
Message-ID: <MWHPR11MB1982F7F0B3C1FAB941284C4597409@MWHPR11MB1982.namprd11.prod.outlook.com> (raw)
In-Reply-To: <c7a09e8d-d2a9-02c9-8ac1-224147bd7827@linux.intel.com>

I thought it would be merged into 5.12 release.  A little disappointed  :< , 
What can I do to help ?

Thanks,
Etan

-----Original Message-----
From: Kuppuswamy, Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> 
Sent: Wednesday, April 28, 2021 8:40 AM
To: Lukas Wunner <lukas@wunner.de>; Bjorn Helgaas <helgaas@kernel.org>; Williams, Dan J <dan.j.williams@intel.com>
Cc: Zhao, Haifeng <haifeng.zhao@intel.com>; Sinan Kaya <okaya@kernel.org>; Raj, Ashok <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

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/59cb30f5e5ac6d65427ceaadf1012b2ba8d
>> bf66c.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

  reply	other threads:[~2021-04-28  1:42 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-28  8:52 Lukas Wunner
2021-03-30 20:53 ` Kuppuswamy, Sathyanarayanan
2021-04-28  0:39   ` Kuppuswamy, Sathyanarayanan
2021-04-28  1:42     ` Zhao, Haifeng [this message]
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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