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

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Message-ID: <20190214020723.GE24589@lunn.ch>
Date:   Thu, 14 Feb 2019 03:07:23 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     John David Anglin <dave.anglin@...l.net>
Cc:     Russell King <linux@....linux.org.uk>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net] dsa: mv88e6xxx: Ensure all pending interrupts are
 handled prior to exit

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.

    Andrew