linux-kernel - Re: [PATCH] PCI: pciehp: Make sure pciehp

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Message-ID: <20191126233735.GA215993@google.com>
Date:   Tue, 26 Nov 2019 17:37:35 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Stuart Hayes <stuart.w.hayes@...il.com>
Cc:     Austin Bolen <austin_bolen@...l.com>, keith.busch@...el.com,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, lukas@...ner.de
Subject: Re: [PATCH] PCI: pciehp: Make sure pciehp_isr clears interrupt events

On Mon, Nov 25, 2019 at 03:03:23PM -0600, Stuart Hayes wrote:
> 
> On 11/12/19 3:59 PM, Stuart Hayes wrote:
> > The pciehp interrupt handler pciehp_isr() will read the slot status
> > register and then write back to it to clear just the bits that caused the
> > interrupt. If a different interrupt event bit gets set between the read and
> > the write, pciehp_isr() will exit without having cleared all of the
> > interrupt event bits, so we will never get another hotplug interrupt from
> > that device.
> > 
> > That is expected behavior according to the PCI Express spec (v.5.0, section
> > 6.7.3.4, "Software Notification of Hot-Plug Events").
> > 
> > Because the "presence detect changed" and "data link layer state changed"
> > event bits are both getting set at nearly the same time when a device is
> > added or removed, this is more likely to happen than it might seem. The
> > issue can be reproduced rather easily by connecting and disconnecting an
> > NVMe device on at least one system model.
> > 
> > This patch fixes the issue by modifying pciehp_isr() to loop back and
> > re-read the slot status register immediately after writing to it, until
> > it sees that all of the event status bits have been cleared.
> > 
> > Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>
> 
> Bjorn,
> 
> Do you have any comments or issues with this patch set?  Anything I can do?

Were you planning to address Lukas' comments?

https://lore.kernel.org/r/20191114025022.wz3gchr7w67fjtzn@wunner.de