linux-kernel - Re: [PATCH net v2 0/1] PHY interruptus horribilis

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Date:   Wed, 8 Jun 2022 13:09:50 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        netdev <netdev@...r.kernel.org>,
        Steve Glendinning <steve.glendinning@...well.net>,
        UNGLinuxDriver@...rochip.com, Oliver Neukum <oneukum@...e.com>,
        Andre Edich <andre.edich@...rochip.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Martyn Welch <martyn.welch@...labora.com>,
        Gabriel Hojda <ghojda@...urs.ro>,
        Christoph Fritz <chf.fritz@...glemail.com>,
        Lino Sanfilippo <LinoSanfilippo@....de>,
        Philipp Rosenberger <p.rosenberger@...bus.com>,
        Ferry Toth <fntoth@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Linux Samsung SoC <linux-samsung-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH net v2 0/1] PHY interruptus horribilis

On Wed, Jun 8, 2022 at 12:35 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Wed, Jun 8, 2022 at 11:52 AM Lukas Wunner <lukas@...ner.de> wrote:
> >
> > Andrew Lunn (PHY maintainer) asked me to resend this patch and cc the
> > IRQ maintainer.  I'm also cc'ing PM maintainers for good measure.
> >
> > The patch addresses an issue with PHY interrupts occurring during a
> > system sleep transition after the PHY has already been suspended.
> >
> > The IRQ subsystem uses an internal flag IRQD_WAKEUP_ARMED to avoid
> > handling such interrupts, but it's not set until suspend_device_irqs()
> > is called during the ->suspend_noirq() phase.  That's too late in this
> > case as PHYs are suspended in the ->suspend() phase.  And there's
> > no external interface to set the flag earlier.
>
> Yes, it is not there intentionally.
>
> Strictly speaking, IRQD_WAKEUP_ARMED is there to indicate to the IRQ
> subsystem that the given IRQ is a system wakeup one and has been left
> enabled specifically in order to signal system wakeup.  It allows the
> IRQ to trigger between suspend_device_irqs() and resume_device_irqs()
> exactly once, which causes the system to wake up from suspend-to-idle
> (that's the primary use case for it) or aborts system suspends in
> progress.
>
> As you have noticed, it is set automatically by suspend_device_irqs()
> if the given IRQ has IRQD_WAKEUP_STATE which is the case when it has
> been enabled for system wakeup.
>
> > As I'm lacking access to the flag, I'm open coding its functionality
> > in this patch.  Is this the correct approach or should I instead look
> > into providing an external interface to the flag?
>
> The idea is that the regular IRQ "action" handler will run before
> suspend_device_irqs(), so it should take care of signaling wakeup if
> need be.  IRQD_WAKEUP_ARMED to trigger wakeup when IRQ "action"
> handlers don't run.

That said IMV there could be a wrapper around suspend_device_irq() to
mark a specific IRQ as "suspended" before running
suspend_device_irqs(), but that would require adding "suspend depth"
to struct irq_desc, so the IRQ is not "resumed" prematurely by
resume_device_irqs().  And there needs to be an analogous wrapper
around resume_irq() for the resume path.

Does the single prospective user justify this?