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

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Date:   Mon, 9 Jul 2018 18:00:08 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Sinan Kaya <Okaya@...nel.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 Mon, Jul 09, 2018 at 08:48:44AM -0600, Sinan Kaya wrote:
> On 7/8/18, Lukas Wunner <lukas@...ner.de> wrote:
> > On Tue, Jul 03, 2018 at 11:43:26AM -0400, Sinan Kaya wrote:
> > > My solution doesn't help if link down interrupt is observed before the
> > > AER
> > > or DPC services.
> >
> > If pciehp gets an interrupt quicker than dpc/aer, it will (at least with
> > my patches) remove all devices, check if the presence bit is set,
> > and if so, try to bring the slot up again.
> 
> Hotplug driver should only observe a link down interrupt. Link would
> come up in response to a secondary bus reset initiated by the AER
> driver.

PCIe hotplug doesn't have separate Link Down and Link Up interrupts,
there is only a Link State *Changed* event.

> Can you point me to the code that would bring up the link in hp code?

I was referring to the situation with my recently posted pciehp patches
applied, in particular patch [21/32] ("PCI: pciehp: Become resilient to
missed events"):
https://patchwork.ozlabs.org/patch/930389/

When I get a presence or link changed event, I turn the slot off.  That
includes removing all devices in the slot.  Because even if the slot is
still occupied or link is up, there was definitely a change and the safe
behavior is to assume that the card in the slot is now a different one
than before.

Afterwards, I check if the slot is occupied or link is up.  If either
of those conditions is true, I try to bring the slot up again.

Thanks,

Lukas