linux-kernel - Re: [PATCH v2 2/4] PCI/DPC/AER: Address Concurrency between AER and DPC

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Message-ID: <c243100f-4fa8-612c-4105-70fda5ce4cde@codeaurora.org>
Date:   Tue, 2 Jan 2018 13:34:52 -0500
From:   Sinan Kaya <okaya@...eaurora.org>
To:     Keith Busch <keith.busch@...el.com>
Cc:     Oza Pawandeep <poza@...eaurora.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dongdong Liu <liudongdong3@...wei.com>,
        Gabriele Paoloni <gabriele.paoloni@...wei.com>,
        Wei Zhang <wzhang@...com>, Timur Tabi <timur@...eaurora.org>
Subject: Re: [PATCH v2 2/4] PCI/DPC/AER: Address Concurrency between AER and
 DPC

On 1/2/2018 12:12 PM, Keith Busch wrote:
> On Tue, Jan 02, 2018 at 08:25:08AM -0500, Sinan Kaya wrote:
>>> 2. A DPC event suppresses the error message required for the Linux
>>> AER driver to run. How can AER and DPC run concurrently?
>>>
>>
>> As we briefly discussed in previous email exchanges, I think you are
>> looking at a use case with a switch that supports DPC functionality. 
> 
> No, I'm interested in DPC in a general.
> 
>> Oza and I are looking at a root port functionality with DPC feature. 
>>
>> As you already know, AER errors are logged to AER capability register
>> independent of the DPC driver presence.
> 
> The error is noted in the Uncorrectable Error Status Register if that's
> what triggered the DPC event. This register has nothing to do with the
> Root Error Status Register, which is required to have received an error
> Message in order to have a status for the AER driver.
> 
>> A root port is also allowed to share the MSI interrupts across DPC and
>> AER. 
>>
>> Therefore, when a DPC interrupt fires; both AER driver and DPC driver
>> starts recovery work. This is the issue we are trying to deal with. 
> 
> If DPC is implemented correctly, the AER Root Status can't have an
> uncorrectable status for the driver to deal with. The only thing the AER
> driver could possibly see is a correctable error if DPC ERR_COR Enable
> is set.
> 
>> In the end, the driver needs to work for both root port and switches.
>> I think you verified it against a switch. We are doing the same for a
>> root port and submitting the plumbing code. 
> 
> I think we need to consider the possibility you are enabling a platform
> that implemented DPC incorrectly. There's nothing in the specification
> that says that DPC enabled root ports are not to discard the error message
> if it came from downstream, or skip signalling the message for root port
> detected errors.
> 

I'll circle this with the HW team.

The current code still doesn't handle outstanding transactions properly.
We can probably split the patch into two and deal with this aspect later.

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.