netdev - Re: [PATCH net] dsa: mv88e6xxx: Ensure all pending interrupts are handled prior to exit

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Date:   Wed, 13 Feb 2019 20:47:31 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     andrew@...n.ch
Cc:     dave.anglin@...l.net, linux@....linux.org.uk,
        vivien.didelot@...oirfairelinux.com, f.fainelli@...il.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net] dsa: mv88e6xxx: Ensure all pending interrupts are
 handled prior to exit

From: Andrew Lunn <andrew@...n.ch>
Date: Thu, 14 Feb 2019 03:07:23 +0100

> On Mon, Feb 11, 2019 at 01:40:21PM -0500, John David Anglin wrote:
>> The GPIO interrupt controller on the espressobin board only supports edge interrupts.
>> If one enables the use of hardware interrupts in the device tree for the 88E6341, it is
>> possible to miss an edge.  When this happens, the INTn pin on the Marvell switch is
>> stuck low and no further interrupts occur.
>> 
>> I found after adding debug statements to mv88e6xxx_g1_irq_thread_work() that there is
>> a race in handling device interrupts (e.g. PHY link interrupts).  Some interrupts are
>> directly cleared by reading the Global 1 status register.  However, the device interrupt
>> flag, for example, is not cleared until all the unmasked SERDES and PHY ports are serviced.
>> This is done by reading the relevant SERDES and PHY status register.
>> 
>> The code only services interrupts whose status bit is set at the time of reading its status
>> register.  If an interrupt event occurs after its status is read and before all interrupts
>> are serviced, then this event will not be serviced and the INTn output pin will remain low.
>> 
>> This is not a problem with polling or level interrupts since the handler will be called
>> again to process the event.  However, it's a big problem when using level interrupts.
>> 
>> The fix presented here is to add a loop around the code servicing switch interrupts.  If
>> any pending interrupts remain after the current set has been handled, we loop and process
>> the new set.  If there are no pending interrupts after servicing, we are sure that INTn has
>> gone high and we will get an edge when a new event occurs.
>> 
>> Tested on espressobin board.
>> 
>> Signed-off-by:  John David Anglin <dave.anglin@...l.net>
> 
> Fixes: dc30c35be720 ("net: dsa: mv88e6xxx: Implement interrupt support.")
> 
> Tested-by: Andrew Lunn <andrew@...n.ch>
> 
> David, please ensure that Heiner's patch:
> 
> net: phy: fix interrupt handling in non-started states
> 
> is applied first. Otherwise we can get into an interrupt storm.

Ok, all done.

Should I queue just this one for -stable?  I didn't queue up Heiner's change for
-stable because it fixes a 5.0-rcX regression.