Re: [PATCH v8 9/9] iio: accel: mma8452: Support interrupt sharing

[Jonathan Cameron]

On Mon, 07 Sep 2026 16:51:04 +0200
Esben Haabendal <esben@xxxxxxxxxx> 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.
> 
> 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.
> 
> Signed-off-by: Esben Haabendal <esben@xxxxxxxxxx>
> ---
>  drivers/iio/accel/mma8452.c | 67 +++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 58 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
> index fda29df5d109..e521dca37f76 100644
> --- a/drivers/iio/accel/mma8452.c
> +++ b/drivers/iio/accel/mma8452.c
> @@ -120,6 +120,7 @@
>   * @sleep_val:			time in ms to sleep while waiting for drdy
>   * @ctrl_reg1:			CTRL_REG1 register shadow value
>   * @data_cfg:			DATA_CFG register shadow value
> + * @ctrl_reg4:			CTRL_REG4 register value to restore on resume
>   * @open_drain:			true for irq pin in open-drain mode
>   */
>  struct mma8452_data {
> @@ -138,6 +139,7 @@ struct mma8452_data {
>  	int sleep_val;
>  	u8 ctrl_reg1;
>  	u8 data_cfg;
> +	u8 ctrl_reg4;
>  	bool open_drain;
>  };
>  
> @@ -1083,15 +1085,21 @@ static irqreturn_t mma8452_interrupt(int irq, void *p)
>  {
>  	struct iio_dev *indio_dev = p;
>  	struct mma8452_data *data = iio_priv(indio_dev);
> +	struct device *dev = &data->client->dev;
>  	irqreturn_t ret = IRQ_NONE;
> +	int pm_status;
>  	int src;
>  
> +	pm_status = pm_runtime_get_if_active(dev);

Sashiko raises the question of what happens if you actually get an error
return from this. You may be deliberately ignoring those, but if
so add a comment.  The fun race around tear down is worth considering
in particular (see sashiko comment).


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

> @@ -1784,29 +1796,62 @@ static void mma8452_remove(struct i2c_client *client)
>  #ifdef CONFIG_PM
>  static int mma8452_runtime_suspend(struct device *dev)
>  {
> -	struct iio_dev *indio_dev = i2c_get_clientdata(to_i2c_client(dev));
> +	struct i2c_client *client = to_i2c_client(dev);
> +	struct iio_dev *indio_dev = i2c_get_clientdata(client);
>  	struct mma8452_data *data = iio_priv(indio_dev);
>  	int ret;
>  
> -	scoped_guard(mutex, &data->lock)
> -		ret = mma8452_standby(data);
> +	guard(mutex)(&data->lock);
Mixing guards... 
> +
> +	ret = i2c_smbus_read_byte_data(client, MMA8452_CTRL_REG4);
>  	if (ret < 0) {
> -		dev_err(dev, "powering off device failed\n");
> +		dev_warn(dev, "backing up CTRL_REG4 failed\n");
>  		return -EAGAIN;
> +	} else
> +		data->ctrl_reg4 = ret;
> +
> +	ret = i2c_smbus_write_byte_data(client, MMA8452_CTRL_REG4, 0);
> +	if (ret) {
> +		dev_warn(dev, "disabling interrupt sources (CTRL_REG4) failed\n");
> +		return -EAGAIN;
> +	}
> +
> +	ret = mma8452_standby(data);
> +	if (ret < 0) {
> +		dev_err(dev, "transition to STANDBY mode failed\n");
> +		ret = -EAGAIN;
> +		goto out_restore_ctrl_reg4;

and goto is explicitly advised against in the docs in cleanup.h
You need to restructure the code to avoid that, potentially via
a helper function.

>  	}
>  
> +	/*
> +	 * Interrupt line should be deasserted now, so we just need ensure any
> +	 * mid-flight irq is completed (will return IRQ_NONE due to
> +	 * pm_status==0).
> +	 */
> +	if (client->irq)
> +		synchronize_irq(client->irq);
> +
>  	ret = regulator_bulk_disable(ARRAY_SIZE(data->regs), data->regs);
>  	if (ret) {
>  		dev_err(dev, "failed to disable regulators\n");
> -		return ret;
> +		goto out_active;
>  	}
>  
>  	return 0;
> +
> +out_active:
> +	if (mma8452_active(data))
> +		dev_warn(dev, "failed to switch back to ACTIVE mode\n");
> +out_restore_ctrl_reg4:
> +	if (i2c_smbus_write_byte_data(client, MMA8452_CTRL_REG4, data->ctrl_reg4))
> +		dev_warn(dev, "restoring CTRL_REG4 failed\n");
> +	return ret;
>  }
>  
>  static int mma8452_runtime_resume(struct device *dev)
>  {
> -	struct iio_dev *indio_dev = i2c_get_clientdata(to_i2c_client(dev));
> +	struct i2c_client *client = to_i2c_client(dev);
> +	struct iio_dev *indio_dev = i2c_get_clientdata(client);
>  	struct mma8452_data *data = iio_priv(indio_dev);
>  	int ret, sleep_val;
>  
> @@ -1820,6 +1865,10 @@ static int mma8452_runtime_resume(struct device *dev)
>  	if (ret)
>  		goto runtime_resume_failed;
>  
> +	ret = i2c_smbus_write_byte_data(client, MMA8452_CTRL_REG4, data->ctrl_reg4);
> +	if (ret)
> +		goto runtime_resume_failed;
> +
>  	ret = mma8452_active(data);
>  	if (ret < 0)
>  		goto runtime_resume_failed;
>