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

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Date:   Tue, 03 Jul 2018 07:30:28 -0400
From:   okaya@...eaurora.org
To:     Lukas Wunner <lukas@...ner.de>
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 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.

I don't think we can skip this step.


> 
> That would seem like a much simpler solution, given that it is known
> that the link will flap on reset, causing the hotplug driver to remove
> and re-enumerate devices.  That would also cover cases where hotplug is
> handled by a different driver than pciehp, or by the platform firmware.
> 
> Thanks,
> 
> Lukas