netdev - Re: [PATCH net-next v3 5/7] usbnet: smsc95xx: Forward PHY interrupts to PHY driver to avoid polling

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Date:   Mon, 6 Jun 2022 03:28:07 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
        linux-usb@...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>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Ferry Toth <fntoth@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        'Linux Samsung SOC' <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH net-next v3 5/7] usbnet: smsc95xx: Forward PHY interrupts
 to PHY driver to avoid polling

> mdio_bus_phy_resume() does trigger the state machine via
> phy_start_machine(), so link state changes *are* detected after wakeup.
> 
> But you're saying that's not sufficient and you really want the
> PHY driver's IRQ handler to be called, do I understand that correctly?

It is an interrupt, so i would expect the handler to be called. I've
never looked deeply how the kernel handles this, but maybe there is
some core support for this. The kernel does know about wake up
interrupts. The interesting bit is how do you defer the interrupt
until you have enough of the system running again you can actually
service the interrupt.

PHY interrupts mostly are level, not edge, because there are multiple
sources of interrupts within the PHY. So you do need to clear the
interrupt source, or you are going to get a storm, as you pointed out.
But being a level might actually help you. It fires once to get you
out of sleep, and then fires again when the interrupt controller is
resumed and is enabled.

	  Andrew