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

[Keith Busch]

On Mon, Mar 12, 2018 at 08:16:38PM +0530, poza@xxxxxxxxxxxxxx wrote:
> 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)

I'm not sure I understand. The link is disabled while DPC is triggered,
so if anything, you'd want to un-enumerate everything below the contained
port (that's what it does today).

After releasing a slot from DPC, the link is allowed to retrain. If there
is a working device on the other side, a link up event occurs. That
event is handled by the pciehp driver, and that schedules enumeration
no matter what you do to the DPC driver.