Subject: Re: [PATCH net-next v9 6/9] net: txgbe: Support GPIO to SFP socket

From: "Russell King (Oracle)" <[email-masked]>
Date: Wed, 24 May 2023 14:07:46 +0100

On Wed, May 24, 2023 at 02:51:25PM +0200, Andrew Lunn wrote:
> > +static void txgbe_toggle_trigger(struct gpio_chip *gc, unsigned int offset)
> > +{
> > +	struct wx *wx = gpiochip_get_data(gc);
> > +	u32 pol, val;
> > +
> > +	pol = rd32(wx, WX_GPIO_POLARITY);
> > +	val = rd32(wx, WX_GPIO_EXT);
> > +
> > +	if (val & BIT(offset))
> > +		pol &= ~BIT(offset);
> > +	else
> > +		pol |= BIT(offset);
> > +
> > +	wr32(wx, WX_GPIO_POLARITY, pol);
> > +}
> 
> So you look at the current state of the GPIO and set the polarity to
> trigger an interrupt when it changes.
> 
> This is not race free. And if it does race, at best you loose an
> interrupt. The worst is your hardware locks up because that interrupt
> was missed and it cannot continue until some action is taken.
> 
> Is there any other GPIO driver doing this?
> 
> I think you would be better indicating you don't support
> IRQ_TYPE_EDGE_BOTH.

... which will make the whole point of having interrupt support for this
driver moot, and the SFP code will then poll the GPIOs which will
probably more reliably detect changes.

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