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Subject: Re: [PATCH] PCI: pciehp: Make sure pciehp_isr clears interrupt events
To:     Bjorn Helgaas <bhelgaas@google.com>
Cc:     Austin Bolen <austin_bolen@dell.com>, keith.busch@intel.com,
        Alexandru Gagniuc <mr.nuke.me@gmail.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Andy Shevchenko <andy.shevchenko@gmail.com>,
        "Gustavo A . R . Silva" <gustavo@embeddedor.com>,
        Sinan Kaya <okaya@kernel.org>,
        Oza Pawandeep <poza@codeaurora.org>, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org, lukas@wunner.de
References: <20191112215938.1145-1-stuart.w.hayes@gmail.com>
From:   Stuart Hayes <stuart.w.hayes@gmail.com>
Message-ID: <a7ac93e3-9a1f-2cd5-bf0b-30b562bd707d@gmail.com>
Date:   Mon, 25 Nov 2019 15:03:23 -0600
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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@gmail.com>

Bjorn,

Do you have any comments or issues with this patch set?  Anything I can do?

Thanks!
Stuart