linux-kernel - Re: [PATCH V5 3/3] PCI: Mask and unmask hotplug interrupts during reset

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Date:   Sun, 29 Jul 2018 14:19:21 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     okaya@...eaurora.org
Cc:     linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Oza Pawandeep <poza@...eaurora.org>,
        Keith Busch <keith.busch@...el.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V5 3/3] PCI: Mask and unmask hotplug interrupts during
 reset

On Tue, Jul 03, 2018 at 07:30:28AM -0400, okaya@...eaurora.org wrote:
> On 2018-07-03 04:34, Lukas Wunner wrote:
> > On Mon, Jul 02, 2018 at 06:52:47PM -0400, Sinan Kaya wrote:
> > > If a bridge supports hotplug and observes a PCIe fatal error, the
> > > following events happen:
> > >
> > > 1. AER driver removes the devices from PCI tree on fatal error
> > > 2. AER driver brings down the link by issuing a secondary bus reset
> > >    waits for the link to come up.
> > > 3. Hotplug driver observes a link down interrupt
> > > 4. Hotplug driver tries to remove the devices waiting for the rescan
> > >    lock but devices are already removed by the AER driver and AER
> > >    driver is waiting for the link to come back up.
> > > 5. AER driver tries to re-enumerate devices after polling for the link
> > >    state to go up.
> > > 6. Hotplug driver obtains the lock and tries to remove the devices
> > >    again.
> > >
> > > If a bridge is a hotplug capable bridge, mask hotplug interrupts
> > > before the reset and unmask afterwards.
> >
> > Would it work for you if you just amended the AER driver to skip
> > removal and re-enumeration of devices if the port is a hotplug bridge?
> > Just check for is_hotplug_bridge in struct pci_dev.
> 
> The reason why we want to remove devices before secondary bus reset is to
> quiesce pcie bus traffic before issuing a reset.
> 
> Skipping this step might cause transactions to be lost in the middle of
> the reset as there will be active traffic flowing and drivers will
> suddenly start reading ffs.

That's par for the course for any hotplug bridge with support for
surprise removal (e.g. Thunderbolt) and drivers must be able to
cope with it.  Nothing to worry about IMHO.

Thanks,

Lukas