linux-kernel - Re: [PATCH v12 0/6] Address error and recovery for AER and DPC

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Date:   Mon, 12 Mar 2018 20:16:38 +0530
From:   poza@...eaurora.org
To:     Keith Busch <keith.busch@...el.com>
Cc:     Sinan Kaya <okaya@...eaurora.org>,
        Bjorn Helgaas <helgaas@...nel.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>,
        Wei Zhang <wzhang@...com>, Timur Tabi <timur@...eaurora.org>,
        linux-pci-owner@...r.kernel.org
Subject: Re: [PATCH v12 0/6] Address error and recovery for AER and DPC

On 2018-03-12 19:55, Keith Busch wrote:
> On Sun, Mar 11, 2018 at 11:03:58PM -0400, Sinan Kaya wrote:
>> On 3/11/2018 6:03 PM, Bjorn Helgaas wrote:
>> > On Wed, Feb 28, 2018 at 10:34:11PM +0530, Oza Pawandeep wrote:
>> 
>> > That difference has been there since the beginning of DPC, so it has
>> > nothing to do with *this* series EXCEPT for the fact that it really
>> > complicates the logic you're adding to reset_link() and
>> > broadcast_error_message().
>> >
>> > We ought to be able to simplify that somehow because the only real
>> > difference between AER and DPC should be that DPC automatically
>> > disables the link and AER does it in software.
>> 
>> I agree this should be possible. Code execution path should be almost
>> identical to fatal error case.
>> 
>> Is there any reason why you went to stop driver path, Keith?
> 
> The fact is the link is truly down during a DPC event. When the link
> is enabled again, you don't know at that point if the device(s) on the
> other side have changed. Calling a driver's error handler for the wrong
> device in an unknown state may have undefined results. Enumerating the
> slot from scratch should be safe, and will assign resources, tune bus
> settings, and bind to the matching driver.
> 
> Per spec, DPC is the recommended way for handling surprise removal
> events and even recommends DPC capable slots *not* set 'Surprise'
> in Slot Capabilities so that removals are always handled by DPC. This
> service driver was developed with that use in mind.

Now it begs the question, that

after DPC trigger

should we enumerate the devices, ?
or
error handling callbacks, followed by stop devices followed by 
enumeration ?
or
error handling callbacks, followed by enumeration ? (no stop devices)

Regards,
Oza.