Re: [PATCH v10 10/10] iio: accel: mma8452: Support interrupt sharing

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Mon, Sep 28, 2026 at 10:26:26AM +0200, Esben Haabendal wrote:
> Adding support for sharing interrupt line with other device requires the
> interrupt handler to handle runtime PM suspension properly, ignoring the
> irq if the device is suspended (maybe even off). And while at it, we use
> the PM reference to ensure we do not get suspended while processing an irq.
> 
> In order to prevent the chip from raising irq while suspended (that is when
> using fixed regulator, where suspend just means setting the device in
> STANDBY mode), we disable all interrupt sources by clearing CTRL_REG4, and
> then restores the value again when resuming.
> 
> The scoped_guard in mma8452_runtime_suspend() is changed to a plain
> mutex_lock() instead, both to prevent mixing guards and goto, but also to
> ensure that we stay in STANDBY mode while writing to CTRL_REG4 and all the
> way up to disabling the device as much as possible.
> 
> With that in place, it is safe to add the IRQF_SHARED flag.
> 
> Keep in mind that the device by default is using push-pull for the irq pin,
> which might require additional hardware design to allow interrupt sharing.

...

> +	pm_status = pm_runtime_get_if_active(dev);
> +	if (pm_status == 0)
> +		/* device is powered down */
> +		return IRQ_NONE;

> +	if (IS_ENABLED(CONFIG_PM) && pm_status < 0)
> +		/* runtime PM was disabled, possibly suspending */
> +		return IRQ_HANDLED;

This is very interesting part. I bet this will be the first driver using this.
A big question "why?"

> +	/*
> +	 * pm_status is now 1 or -EINVAL (with CONFIG_PM not enabled). If
> +	 * pm_status==1, runtime PM is enabled and device is RPM_ACTIVE. If
> +	 * pm_status==-EINVAL, runtime PM is build-time disabled (i.e. CONFIG_PM
> +	 * not enabled), and we can/must assume device is active.
> +	 */
> +
>  	src = i2c_smbus_read_byte_data(data->client, MMA8452_INT_SRC);
>  	if (src < 0)
> -		return IRQ_NONE;
> +		goto out_runtime_put;
>  
>  	if (!(src & (data->chip_info->enabled_events | MMA8452_INT_DRDY)))
> -		return IRQ_NONE;
> +		goto out_runtime_put;
>  
>  	if (src & MMA8452_INT_DRDY) {
>  		iio_trigger_poll_nested(indio_dev->trig);
> @@ -1120,6 +1139,10 @@ static irqreturn_t mma8452_interrupt(int irq, void *p)
>  		ret = IRQ_HANDLED;
>  	}
>  
> +out_runtime_put:
> +	if (pm_status > 0)
> +		pm_runtime_put_autosuspend(dev);
> +
>  	return ret;
>  }

...

> +	pm_runtime_enable(dev);
> +	pm_runtime_set_autosuspend_delay(dev, MMA8452_AUTO_SUSPEND_DELAY_MS);
> +	pm_runtime_use_autosuspend(dev);

I don't see the respective _dont_use_autosuspend() call anywhere.

...

I am wondering how many of the above possible scenarios you were able to test.

...

P.S.  I bet you can now make a presentation "PM runtime in Linux and
why it is so hard."

-- 
With Best Regards,
Andy Shevchenko