From: Lukas Wunner <lukas@wunner.de>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Eric Dumazet <edumazet@google.com>,
netdev@vger.kernel.org, linux-usb@vger.kernel.org,
Steve Glendinning <steve.glendinning@shawell.net>,
UNGLinuxDriver@microchip.com, Oliver Neukum <oneukum@suse.com>,
Andre Edich <andre.edich@microchip.com>,
Oleksij Rempel <linux@rempel-privat.de>,
Martyn Welch <martyn.welch@collabora.com>,
Gabriel Hojda <ghojda@yo2urs.ro>,
Christoph Fritz <chf.fritz@googlemail.com>,
Lino Sanfilippo <LinoSanfilippo@gmx.de>,
Philipp Rosenberger <p.rosenberger@kunbus.com>,
Heiner Kallweit <hkallweit1@gmail.com>,
Russell King <linux@armlinux.org.uk>,
Ferry Toth <fntoth@gmail.com>,
Krzysztof Kozlowski <krzk@kernel.org>,
'Linux Samsung SOC' <linux-samsung-soc@vger.kernel.org>
Subject: Re: [PATCH net-next v3 5/7] usbnet: smsc95xx: Forward PHY interrupts to PHY driver to avoid polling
Date: Mon, 23 May 2022 15:47:09 +0200 [thread overview]
Message-ID: <20220523134709.GA25989@wunner.de> (raw)
In-Reply-To: <Yot/ad/Ch7iGYnGB@lunn.ch>
On Mon, May 23, 2022 at 02:34:49PM +0200, Andrew Lunn wrote:
> > --- a/drivers/net/phy/phy_device.c
> > +++ b/drivers/net/phy/phy_device.c
> > @@ -283,8 +283,11 @@ static __maybe_unused int mdio_bus_phy_suspend(struct device *dev)
> > * may call phy routines that try to grab the same lock, and that may
> > * lead to a deadlock.
> > */
> > - if (phydev->attached_dev && phydev->adjust_link)
> > + if (phydev->attached_dev && phydev->adjust_link) {
> > + if (phy_interrupt_is_valid(phydev))
> > + synchronize_irq(phydev->irq);
> > phy_stop_machine(phydev);
> > + }
>
> What is this hunk trying to achieve? As far as i know, interrupts have
> not been disabled. So as soon as the call to synchronize_irq()
> finishes, could well be another interrupt happens.
That other interrupt would bail out of phy_interrupt() because
the is_prepared flag is set on the PHY's struct device, see
first hunk of the patch.
The problem is that an interrupt may occur before the system
sleep transition commences. phy_interrupt() will notice that
is_prepared is not (yet) set, hence invokes drv->handle_interrupt().
Let's say the IRQ thread is preempted at that point, the system
sleep transition is started and mdio_bus_phy_suspend() is run.
It calls phy_stop_machine(), so the state machine is now stopped.
Now phy_interrupt() continues, and the PHY driver's ->handle_interrupt()
callback starts the state machine. Boom, that's not what we want.
So the synchronize_irq() ensures that any already running
phy_interrupt() runs to completion before phy_stop_machine()
is called. It doesn't matter if another interrupt occurs
because then is_prepared will have been set and therefore
phy_interrupt() won't call drv->handle_interrupt().
Let me know if I haven't explained it in sufficient clarity,
I'll be happy to try again. :)
I'm more concerned about the first hunk of the patch because I'm
not sure I got the wakeup stuff right...
Thanks,
Lukas
next prev parent reply other threads:[~2022-05-23 13:47 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1652343655.git.lukas@wunner.de>
[not found] ` <748ac44eeb97b209f66182f3788d2a49d7bc28fe.1652343655.git.lukas@wunner.de>
[not found] ` <CGME20220517101846eucas1p2c132f7e7032ed00996e222e9cc6cdf99@eucas1p2.samsung.com>
2022-05-17 10:18 ` [PATCH net-next v3 5/7] usbnet: smsc95xx: Forward PHY interrupts to PHY driver to avoid polling Marek Szyprowski
2022-05-19 19:08 ` Lukas Wunner
2022-05-19 21:22 ` Marek Szyprowski
2022-05-23 9:43 ` Lukas Wunner
2022-05-23 11:38 ` Marek Szyprowski
2022-05-23 12:34 ` Andrew Lunn
2022-05-23 13:47 ` Lukas Wunner [this message]
2022-05-24 0:52 ` Andrew Lunn
2022-05-24 1:08 ` Andrew Lunn
2022-05-24 6:16 ` Marek Szyprowski
2022-05-24 12:03 ` Andrew Lunn
2022-05-26 13:55 ` Lukas Wunner
2022-05-24 12:13 ` Lukas Wunner
2022-06-06 1:28 ` Andrew Lunn
2022-08-26 6:51 ` Marek Szyprowski
2022-08-26 7:19 ` Lukas Wunner
2022-08-26 7:41 ` Marek Szyprowski
2022-08-26 7:53 ` Lukas Wunner
2022-08-26 8:29 ` Marek Szyprowski
2022-08-29 11:40 ` Marek Szyprowski
2022-09-18 19:13 ` Lukas Wunner
2022-09-18 20:41 ` Florian Fainelli
2022-09-18 20:55 ` Lukas Wunner
2022-09-18 22:11 ` Florian Fainelli
2022-09-23 4:20 ` Lukas Wunner
2022-09-22 13:21 ` Marek Szyprowski
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