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Date:   Mon, 1 Jun 2020 20:46:48 +0000
From:   "Agarwal, Anchal" <anchalag@...zon.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "jgross@...e.com" <jgross@...e.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Kamata, Munehisa" <kamatam@...zon.com>,
        "sstabellini@...nel.org" <sstabellini@...nel.org>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "roger.pau@...rix.com" <roger.pau@...rix.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "len.brown@...el.com" <len.brown@...el.com>,
        "pavel@....cz" <pavel@....cz>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Valentin, Eduardo" <eduval@...zon.com>,
        "Singh, Balbir" <sblbir@...zon.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>
Subject: Re: [PATCH 05/12] genirq: Shutdown irq chips in suspend/resume during
 hibernation


    CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.



    On 5/19/20 7:26 PM, Anchal Agarwal wrote:
    > Many legacy device drivers do not implement power management (PM)
    > functions which means that interrupts requested by these drivers stay
    > in active state when the kernel is hibernated.
    >
    > This does not matter on bare metal and on most hypervisors because the
    > interrupt is restored on resume without any noticable side effects as
    > it stays connected to the same physical or virtual interrupt line.
    >
    > The XEN interrupt mechanism is different as it maintains a mapping
    > between the Linux interrupt number and a XEN event channel. If the
    > interrupt stays active on hibernation this mapping is preserved but
    > there is unfortunately no guarantee that on resume the same event
    > channels are reassigned to these devices. This can result in event
    > channel conflicts which prevent the affected devices from being
    > restored correctly.
    >
    > One way to solve this would be to add the necessary power management
    > functions to all affected legacy device drivers, but that's a
    > questionable effort which does not provide any benefits on non-XEN
    > environments.
    >
    > The least intrusive and most efficient solution is to provide a
    > mechanism which allows the core interrupt code to tear down these
    > interrupts on hibernation and bring them back up again on resume. This
    > allows the XEN event channel mechanism to assign an arbitrary event
    > channel on resume without affecting the functionality of these
    > devices.
    >
    > Fortunately all these device interrupts are handled by a dedicated XEN
    > interrupt chip so the chip can be marked that all interrupts connected
    > to it are handled this way. This is pretty much in line with the other
    > interrupt chip specific quirks, e.g. IRQCHIP_MASK_ON_SUSPEND.
    >
    > Add a new quirk flag IRQCHIP_SHUTDOWN_ON_SUSPEND and add support for
    > it the core interrupt suspend/resume paths.
    >
    > Signed-off-by: Anchal Agarwal <anchalag@...zon.com>
    > Signed-off--by: Thomas Gleixner <tglx@...utronix.de>


    Since Thomas wrote this patch I think it should also have "From: " him.

That sounds about right. I will update it next round and add Tested-by.

    -boris

- Anchal



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