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Subject: Re: [PATCH v2] 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: <20191120222043.53432-1-stuart.w.hayes@gmail.com>
From:   Stuart Hayes <stuart.w.hayes@gmail.com>
Message-ID: <41285254-1bc1-3ffe-383e-276dc7193990@gmail.com>
Date:   Mon, 20 Jan 2020 10:10:11 -0600
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On 11/20/19 4:20 PM, Stuart Hayes wrote:
> Without this patch, a pciehp hotplug port can stop generating interrupts
> on hotplug events, so device adds and removals will not be seen.
> 
> The pciehp interrupt handler pciehp_isr() will read the slot status
> register and then write back to it to clear 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. If this happens, and the port is using an MSI interrupt where
> per-vector masking is not supported, we won't get any more hotplug
> interrupts from that device.
> 
> That is expected behavior, according to the PCI Express Base Specification
> Revision 5.0 Version 1.0, 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 was found (and can be reproduced rather easily) by connecting and
> disconnecting an NVMe storage device on at least one system model.
> 
> This issue was found while adding and removing various NVMe storage devices
> on an AMD PCIe port (PCI device 0x1022/0x1483).
> 
> This patch fixes this issue by modifying pciehp_isr() by looping back and
> re-reading 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>
> ---
> v2:
>   * fixed ctrl_warn() call
>   * improved comments
>   * added pvm_capable flag and changed pciehp_isr() to loop back only when
>     pvm_capable flag not set (suggested by Lukas Wunner)
>   
>  drivers/pci/hotplug/pciehp.h     |  3 ++
>  drivers/pci/hotplug/pciehp_hpc.c | 50 ++++++++++++++++++++++++++++----
>  2 files changed, 47 insertions(+), 6 deletions(-)
> 

Bjorn,

Please let me know if I could do anything to help get this patch accepted.

Thanks!
Stuart