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Subject: Re: [PATCH 05/12] genirq: Shutdown irq chips in suspend/resume during
 hibernation
To:     Anchal Agarwal <anchalag@amazon.com>, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org,
        jgross@suse.com, linux-pm@vger.kernel.org, linux-mm@kvack.org,
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        roger.pau@citrix.com, axboe@kernel.dk, davem@davemloft.net,
        rjw@rjwysocki.net, len.brown@intel.com, pavel@ucw.cz,
        peterz@infradead.org, eduval@amazon.com, sblbir@amazon.com,
        xen-devel@lists.xenproject.org, vkuznets@redhat.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        dwmw@amazon.co.uk, benh@kernel.crashing.org
References: <cover.1589926004.git.anchalag@amazon.com>
 <fce013fc1348f02b8e4ec61e7a631093c72f993c.1589926004.git.anchalag@amazon.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Message-ID: <0471e6e3-b6ed-d2c6-db41-1688a0af9abd@oracle.com>
Date:   Sat, 30 May 2020 19:17:41 -0400
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@amazon.com>
> Signed-off--by: Thomas Gleixner <tglx@linutronix.de>


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


-boris