netdev - Re: [PATCH net-next v2 2/3] net: phy: add callback for custom interrupt handler to struct phy

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Date:   Tue, 19 Nov 2019 11:33:47 +0100
From:   Michael Walle <michael@...le.cc>
To:     hkallweit1@...il.com
Cc:     andrew@...n.ch, davem@...emloft.net, f.fainelli@...il.com,
        linux@...linux.org.uk, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 2/3] net: phy: add callback for custom
 interrupt handler to struct phy_driver

Hi,

this is an old thread and I know its already applied. But I'd like to 
hear your opinion on the following problem below.

> The phylib interrupt handler handles link change events only currently.
> However PHY drivers may want to use other interrupt sources too,
> e.g. to report temperature monitoring events. Therefore add a callback
> to struct phy_driver allowing PHY drivers to implement a custom
> interrupt handler.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> Suggested-by: Russell King - ARM Linux admin <linux@...linux.org.uk>
> Acked-by: Russell King <rmk+kernel@...linux.org.uk>
> ---
>  drivers/net/phy/phy.c | 9 +++++++--
>  include/linux/phy.h   | 3 +++
>  2 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
> index d90d9863e..068f0a126 100644
> --- a/drivers/net/phy/phy.c
> +++ b/drivers/net/phy/phy.c
> @@ -772,8 +772,13 @@ static irqreturn_t phy_interrupt(int irq, void 
> *phy_dat)
>  	if (phydev->drv->did_interrupt && 
> !phydev->drv->did_interrupt(phydev))
>  		return IRQ_NONE;
> 
> -	/* reschedule state queue work to run as soon as possible */
> -	phy_trigger_machine(phydev);
> +	if (phydev->drv->handle_interrupt) {
> +		if (phydev->drv->handle_interrupt(phydev))
> +			goto phy_err;

There are PHYs which clears the interrupt already by reading the 
interrupt status register. To do something useful in handle_interrupt() 
I have to read the interrupt status register, thus clearing the pending 
interrupts.

> +	} else {
> +		/* reschedule state queue work to run as soon as possible */
> +		phy_trigger_machine(phydev);
> +	}
> 
>  	if (phy_clear_interrupt(phydev))
>  		goto phy_err;

But here the interrupts are cleared again, which means we might loose 
interrupt causes in between.

I could think of two different fixes:
  (1) handle_interrupt() has to take care to clear the interrupts and 
skip the phy_clear_interrupt() above.
  (2) handle_interrupt() might return a special return code which skips 
the phy_clear_interrupt

TBH, I'd prefer (1) but I don't know if it is allowed to change 
semantics afterwards. (Also, I've found no driver where 
handle_interrupt() is actually used for now?)

-michael