netdev - Re: [PATCH net] net: phy: avoid clearing PHY interrupts twice in irq handler

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Date:   Mon, 2 Mar 2020 00:20:41 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Michael Walle <michael@...le.cc>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net] net: phy: avoid clearing PHY interrupts twice in irq
 handler

On 01.03.2020 23:52, Michael Walle wrote:
> Am 2020-03-01 21:36, schrieb Heiner Kallweit:
>> On all PHY drivers that implement did_interrupt() reading the interrupt
>> status bits clears them. This means we may loose an interrupt that
>> is triggered between calling did_interrupt() and phy_clear_interrupt().
>> As part of the fix make it a requirement that did_interrupt() clears
>> the interrupt.
> 
> Looks good. But how would you use did_interrupt() and handle_interrupt()
> together? I guess you can't. At least not if handle_interrupt() has
> to read the pending bits again. So you'd have to handle custom
> interrupts in did_interrupt(). Any idea how to solve that?
> 
> [I know, this is only about fixing the lost interrupts.]
> 
Right, this one is meant for stable to fix the issue with the potentially
lost interrupts. Based on it I will submit a patch for net-next that
tackles the issue that did_interrupt() has to read (and therefore clear)
irq status bits and therefore makes them unusable for handle_interrupt().
The basic idea is that did_interrupt() is called only if handle_interrupt()
isn't implemented. handle_interrupt() has to include the did_interrupt
functionality. It can read the irq status once and store it in a variable
for later use.

> -michael
> 
>>
>> The Fixes tag refers to the first commit where the patch applies
>> cleanly.
>>
>> Fixes: 49644e68f472 ("net: phy: add callback for custom interrupt
>> handler to struct phy_driver")
>> Reported-by: Michael Walle <michael@...le.cc>
>> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
>> ---
>>  drivers/net/phy/phy.c | 3 ++-
>>  include/linux/phy.h   | 1 +
>>  2 files changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
>> index d76e038cf..16e3fb79e 100644
>> --- a/drivers/net/phy/phy.c
>> +++ b/drivers/net/phy/phy.c
>> @@ -727,7 +727,8 @@ static irqreturn_t phy_interrupt(int irq, void *phy_dat)
>>          phy_trigger_machine(phydev);
>>      }
>>
>> -    if (phy_clear_interrupt(phydev))
>> +    /* did_interrupt() may have cleared the interrupt already */
>> +    if (!phydev->drv->did_interrupt && phy_clear_interrupt(phydev))
>>          goto phy_err;
>>      return IRQ_HANDLED;
>>
>> diff --git a/include/linux/phy.h b/include/linux/phy.h
>> index 80f8b2158..8b299476b 100644
>> --- a/include/linux/phy.h
>> +++ b/include/linux/phy.h
>> @@ -557,6 +557,7 @@ struct phy_driver {
>>      /*
>>       * Checks if the PHY generated an interrupt.
>>       * For multi-PHY devices with shared PHY interrupt pin
>> +     * Set interrupt bits have to be cleared.
>>       */
>>      int (*did_interrupt)(struct phy_device *phydev);