[PATCH v4 0/6] io: accel: mma8452: Allow open drain interrupt pin configuration

[PATCH v4 0/6] io: accel: mma8452: Allow open drain interrupt pin configuration

[Esben Haabendal]

Extend the mma8452 driver with support for configuration of the
interrupt line in open-drain mode, which is needed for hardware designs
where the interrupt line is shared with other chips.

Adding drive-open-drain property to mma8452 device-tree node for such
designs to enable switching pin configuration to open-drain mode.

Signed-off-by: Esben Haabendal <esben@geanix.com>
---
Changes in v4:
- Fixed interrupt handler to check runtime PM status before trying to
  access the chip.
- Split open-drain support and interrupt sharing into separate patches.
- Added new patch to reuse existing struct device * through mma8452_probe()
  function.
- Print warning message when irq type is not set by firmware.
- Link to v3: https://patch.msgid.link/20260805-mma8452-open-drain-v3-0-6149f406a409@geanix.com

Changes in v3:
- Reordered patches, swapping #2 and #3.
- Always add IRQF_SHARED flag.
- New patch to change it so IQRF_TRIGGER_LOW flag is only added when no
  trigger type is set by firmware.
- Link to v2: https://patch.msgid.link/20260715-mma8452-open-drain-v2-0-95be9f5f4795@geanix.com

Changes in v2:
- Commit message of patch 2 updated.
- Operator precedence bug fixed in flags argument to
  request_threaded_irq().
- Always check return value of mma8452_set_interrupt_pin_mode(), and just
  check for non-zero value.
- Added new patch with optimization of struct mma8452_data ordering.
- Link to v1: https://patch.msgid.link/20260715-mma8452-open-drain-v1-0-b1dd2a440c60@geanix.com

To: Jonathan Cameron <jic23@kernel.org>
To: Lars-Peter Clausen <lars@metafoo.de>
To: Rob Herring <robh@kernel.org>
To: Krzysztof Kozlowski <krzk+dt@kernel.org>
To: Conor Dooley <conor+dt@kernel.org>
To: Martin Kepplinger <martink@posteo.de>
To: Sean Nyekjaer <sean@geanix.com>
To: David Lechner <dlechner@baylibre.com>
To: Nuno Sá <nuno.sa@analog.com>
To: Andy Shevchenko <andy@kernel.org>
To: Martin Kepplinger <martin.kepplinger@theobroma-systems.com>
Cc: linux-iio@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

---
Esben Haabendal (6):
      dt-bindings: iio: accel: mma8452: Add drive-open-drain
      iio: accel: mma8452: Optimize struct mm8452_data member orders
      iio: accel: mma8452: Only apply trigger type when not set by firmware
      iio: accel: mma8452: Support interrupt sharing
      iio: accel: mma8452: Allow open drain interrupt pin configuration
      iio: accel: mma8452: Reuse existing dev pointer in mma8452_probe()

 .../devicetree/bindings/iio/accel/fsl,mma8452.yaml |  6 ++
 drivers/iio/accel/mma8452.c                        | 90 ++++++++++++++++------
 2 files changed, 73 insertions(+), 23 deletions(-)
---
base-commit: db2ddb87143519e20a95aa36c60b36107b736a58
change-id: 20250401-mma8452-open-drain-81577c41375c

Best regards,
--  
Esben Haabendal <esben@geanix.com>

[PATCH v4 1/6] dt-bindings: iio: accel: mma8452: Add drive-open-drain

[Esben Haabendal]

Add new boolean to configure selected interrupt pin to open drain instead
of the default push-pull mode.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Esben Haabendal <esben@geanix.com>
---
 Documentation/devicetree/bindings/iio/accel/fsl,mma8452.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/accel/fsl,mma8452.yaml b/Documentation/devicetree/bindings/iio/accel/fsl,mma8452.yaml
index b0dd2b4e116a..20701aa725d0 100644
--- a/Documentation/devicetree/bindings/iio/accel/fsl,mma8452.yaml
+++ b/Documentation/devicetree/bindings/iio/accel/fsl,mma8452.yaml
@@ -39,6 +39,12 @@ properties:
     minItems: 1
     maxItems: 2
 
+  drive-open-drain:
+    $ref: /schemas/types.yaml#/definitions/flag
+    description: the interrupt line will be configured as open drain, which is
+      useful if several sensors share the same interrupt line. (This binding is
+      taken from pinctrl.)
+
   vdd-supply: true
   vddio-supply: true
 

-- 
2.55.0

[PATCH v4 2/6] iio: accel: mma8452: Optimize struct mm8452_data member orders

[Esben Haabendal]

Reorder struct mma8452_data members to avoid holes.

Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Esben Haabendal <esben@geanix.com>
---
 drivers/iio/accel/mma8452.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
index 7d683686dd9d..f645a5c6fd1c 100644
--- a/drivers/iio/accel/mma8452.c
+++ b/drivers/iio/accel/mma8452.c
@@ -106,10 +106,7 @@ struct mma8452_data {
 	struct i2c_client *client;
 	struct mutex lock;
 	struct iio_mount_matrix orientation;
-	u8 ctrl_reg1;
-	u8 data_cfg;
 	const struct mma_chip_info *chip_info;
-	int sleep_val;
 	struct regulator *vdd_reg;
 	struct regulator *vddio_reg;
 
@@ -118,6 +115,10 @@ struct mma8452_data {
 		__be16 channels[3];
 		aligned_s64 ts;
 	} buffer;
+
+	int sleep_val;
+	u8 ctrl_reg1;
+	u8 data_cfg;
 };
 
  /**

-- 
2.55.0

[PATCH v4 3/6] iio: accel: mma8452: Only apply trigger type when not set by firmware

[Esben Haabendal]

Instead of unconditionally overriding the trigger type, it is better to
only apply a default when no trigger type is set by firmware. This should
be reasonably backward compatible, and should only potentially cause
problems if systems exist where firmware specifies an incorrect trigger
type. With a bit of luck, there are no such systems.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Esben Haabendal <esben@geanix.com>
---
 drivers/iio/accel/mma8452.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
index f645a5c6fd1c..1fb43c5b0b72 100644
--- a/drivers/iio/accel/mma8452.c
+++ b/drivers/iio/accel/mma8452.c
@@ -1683,9 +1683,16 @@ static int mma8452_probe(struct i2c_client *client)
 		goto trigger_cleanup;
 
 	if (client->irq) {
+		unsigned long irq_flags;
+
+		irq_flags = irq_get_trigger_type(client->irq);
+		if (irq_flags == IRQ_TYPE_NONE) {
+			dev_info(dev, "invalid irq type, setting default active low\n");
+			irq_flags = IRQF_TRIGGER_LOW;
+		}
+		irq_flags |= IRQF_ONESHOT;
 		ret = request_threaded_irq(client->irq, NULL, mma8452_interrupt,
-					   IRQF_TRIGGER_LOW | IRQF_ONESHOT,
-					   client->name, indio_dev);
+					   irq_flags, client->name, indio_dev);
 		if (ret)
 			goto buffer_cleanup;
 	}

-- 
2.55.0

[PATCH v4 4/6] iio: accel: mma8452: Support interrupt sharing

[Esben Haabendal]

Adding handling of rutnime PM suspension in the interrupt handler allows
sharing interrupt with other devices.

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@geanix.com>
---
 drivers/iio/accel/mma8452.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
index 1fb43c5b0b72..106cdd904dbf 100644
--- a/drivers/iio/accel/mma8452.c
+++ b/drivers/iio/accel/mma8452.c
@@ -1056,14 +1056,19 @@ static irqreturn_t mma8452_interrupt(int irq, void *p)
 	struct iio_dev *indio_dev = p;
 	struct mma8452_data *data = iio_priv(indio_dev);
 	irqreturn_t ret = IRQ_NONE;
+	int pm_status;
 	int src;
 
+	pm_status = pm_runtime_get_if_active(&data->client->dev);
+	if (pm_status == 0)
+		return IRQ_NONE; /* device is powered down */
+
 	src = i2c_smbus_read_byte_data(data->client, MMA8452_INT_SRC);
 	if (src < 0)
-		return IRQ_NONE;
+		goto out;
 
 	if (!(src & (data->chip_info->enabled_events | MMA8452_INT_DRDY)))
-		return IRQ_NONE;
+		goto out;
 
 	if (src & MMA8452_INT_DRDY) {
 		iio_trigger_poll_nested(indio_dev->trig);
@@ -1089,6 +1094,10 @@ static irqreturn_t mma8452_interrupt(int irq, void *p)
 		ret = IRQ_HANDLED;
 	}
 
+out:
+	if (pm_status > 0)
+		pm_runtime_put_autosuspend(&data->client->dev);
+
 	return ret;
 }
 
@@ -1690,7 +1699,7 @@ static int mma8452_probe(struct i2c_client *client)
 			dev_info(dev, "invalid irq type, setting default active low\n");
 			irq_flags = IRQF_TRIGGER_LOW;
 		}
-		irq_flags |= IRQF_ONESHOT;
+		irq_flags |= IRQF_ONESHOT | IRQF_SHARED;
 		ret = request_threaded_irq(client->irq, NULL, mma8452_interrupt,
 					   irq_flags, client->name, indio_dev);
 		if (ret)

-- 
2.55.0

[PATCH v4 5/6] iio: accel: mma8452: Allow open drain interrupt pin configuration

[Esben Haabendal]

When designing systems sharing the interrupt for mma8452 chips, it is
helpful to be able to configure the irq pin in open-drain mode (default is
push-pull).

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Esben Haabendal <esben@geanix.com>
---
 drivers/iio/accel/mma8452.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
index 106cdd904dbf..7992f9e38818 100644
--- a/drivers/iio/accel/mma8452.c
+++ b/drivers/iio/accel/mma8452.c
@@ -81,6 +81,8 @@
 #define  MMA8452_CTRL_REG2_RST			BIT(6)
 #define  MMA8452_CTRL_REG2_MODS_SHIFT		3
 #define  MMA8452_CTRL_REG2_MODS_MASK		0x1b
+#define MMA8452_CTRL_REG3			0x2c
+#define  MMA8452_CTRL_REG3_PP_OD		BIT(0)
 #define MMA8452_CTRL_REG4			0x2d
 #define MMA8452_CTRL_REG5			0x2e
 #define MMA8452_OFF_X				0x2f
@@ -119,6 +121,7 @@ struct mma8452_data {
 	int sleep_val;
 	u8 ctrl_reg1;
 	u8 data_cfg;
+	bool open_drain;
 };
 
  /**
@@ -647,6 +650,22 @@ static int mma8452_set_power_mode(struct mma8452_data *data, u8 mode)
 	return mma8452_change_config(data, MMA8452_CTRL_REG2, reg);
 }
 
+static int mma8452_set_interrupt_pin_mode(struct mma8452_data *data)
+{
+	int reg;
+
+	reg = i2c_smbus_read_byte_data(data->client, MMA8452_CTRL_REG3);
+	if (reg < 0)
+		return reg;
+
+	if (data->open_drain)
+		reg |= MMA8452_CTRL_REG3_PP_OD;
+	else
+		reg &= ~MMA8452_CTRL_REG3_PP_OD;
+
+	return i2c_smbus_write_byte_data(data->client, MMA8452_CTRL_REG3, reg);
+}
+
 /* returns >0 if in freefall mode, 0 if not or <0 if an error occurred */
 static int mma8452_freefall_mode_enabled(struct mma8452_data *data)
 {
@@ -1676,6 +1695,11 @@ static int mma8452_probe(struct i2c_client *client)
 			goto disable_regulators;
 	}
 
+	data->open_drain = device_property_read_bool(dev, "drive-open-drain");
+	ret = mma8452_set_interrupt_pin_mode(data);
+	if (ret)
+		goto trigger_cleanup;
+
 	data->ctrl_reg1 = MMA8452_CTRL_ACTIVE |
 			  (MMA8452_CTRL_DR_DEFAULT << MMA8452_CTRL_DR_SHIFT);
 
@@ -1817,6 +1841,10 @@ static int mma8452_runtime_resume(struct device *dev)
 		return ret;
 	}
 
+	ret = mma8452_set_interrupt_pin_mode(data);
+	if (ret)
+		goto runtime_resume_failed;
+
 	ret = mma8452_active(data);
 	if (ret < 0)
 		goto runtime_resume_failed;

-- 
2.55.0

[PATCH v4 6/6] iio: accel: mma8452: Reuse existing dev pointer in mma8452_probe()

[Esben Haabendal]

In commit 32a5c04d4575 ("iio: accel: mma8452: Use dev_err_probe()") the
struct device * pointer was assigned to local variable dev, so we can just
as well reuse that throughout the function for sligthly more readable code.

Signed-off-by: Esben Haabendal <esben@geanix.com>
---
 drivers/iio/accel/mma8452.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
index 7992f9e38818..2fbf9f9ed9d7 100644
--- a/drivers/iio/accel/mma8452.c
+++ b/drivers/iio/accel/mma8452.c
@@ -1581,7 +1581,7 @@ static int mma8452_probe(struct i2c_client *client)
 	struct iio_dev *indio_dev;
 	int ret;
 
-	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
 	if (!indio_dev)
 		return -ENOMEM;
 
@@ -1591,21 +1591,21 @@ static int mma8452_probe(struct i2c_client *client)
 
 	data->chip_info = i2c_get_match_data(client);
 	if (!data->chip_info)
-		return dev_err_probe(&client->dev, -ENODEV,
+		return dev_err_probe(dev, -ENODEV,
 				     "unknown device model\n");
 
-	ret = iio_read_mount_matrix(&client->dev, &data->orientation);
+	ret = iio_read_mount_matrix(dev, &data->orientation);
 	if (ret)
 		return ret;
 
-	data->vdd_reg = devm_regulator_get(&client->dev, "vdd");
+	data->vdd_reg = devm_regulator_get(dev, "vdd");
 	if (IS_ERR(data->vdd_reg))
-		return dev_err_probe(&client->dev, PTR_ERR(data->vdd_reg),
+		return dev_err_probe(dev, PTR_ERR(data->vdd_reg),
 				     "failed to get VDD regulator!\n");
 
-	data->vddio_reg = devm_regulator_get(&client->dev, "vddio");
+	data->vddio_reg = devm_regulator_get(dev, "vddio");
 	if (IS_ERR(data->vddio_reg))
-		return dev_err_probe(&client->dev, PTR_ERR(data->vddio_reg),
+		return dev_err_probe(dev, PTR_ERR(data->vddio_reg),
 				     "failed to get VDDIO regulator!\n");
 
 	ret = regulator_enable(data->vdd_reg);
@@ -1637,7 +1637,7 @@ static int mma8452_probe(struct i2c_client *client)
 		goto disable_regulators;
 	}
 
-	dev_info(&client->dev, "registering %s accelerometer; ID 0x%x\n",
+	dev_info(dev, "registering %s accelerometer; ID 0x%x\n",
 		 data->chip_info->name, data->chip_info->chip_id);
 
 	i2c_set_clientdata(client, indio_dev);
@@ -1670,10 +1670,10 @@ static int mma8452_probe(struct i2c_client *client)
 	if (client->irq) {
 		int irq2;
 
-		irq2 = fwnode_irq_get_byname(dev_fwnode(&client->dev), "INT2");
+		irq2 = fwnode_irq_get_byname(dev_fwnode(dev), "INT2");
 
 		if (irq2 == client->irq) {
-			dev_dbg(&client->dev, "using interrupt line INT2\n");
+			dev_dbg(dev, "using interrupt line INT2\n");
 		} else {
 			ret = i2c_smbus_write_byte_data(client,
 							MMA8452_CTRL_REG5,
@@ -1681,7 +1681,7 @@ static int mma8452_probe(struct i2c_client *client)
 			if (ret < 0)
 				goto disable_regulators;
 
-			dev_dbg(&client->dev, "using interrupt line INT1\n");
+			dev_dbg(dev, "using interrupt line INT1\n");
 		}
 
 		ret = i2c_smbus_write_byte_data(client,
@@ -1730,14 +1730,13 @@ static int mma8452_probe(struct i2c_client *client)
 			goto buffer_cleanup;
 	}
 
-	ret = pm_runtime_set_active(&client->dev);
+	ret = pm_runtime_set_active(dev);
 	if (ret < 0)
 		goto free_irq;
 
-	pm_runtime_enable(&client->dev);
-	pm_runtime_set_autosuspend_delay(&client->dev,
-					 MMA8452_AUTO_SUSPEND_DELAY_MS);
-	pm_runtime_use_autosuspend(&client->dev);
+	pm_runtime_enable(dev);
+	pm_runtime_set_autosuspend_delay(dev, MMA8452_AUTO_SUSPEND_DELAY_MS);
+	pm_runtime_use_autosuspend(dev);
 
 	ret = iio_device_register(indio_dev);
 	if (ret < 0)

-- 
2.55.0

Re: [PATCH v4 6/6] iio: accel: mma8452: Reuse existing dev pointer in mma8452_probe()

[Andy Shevchenko]

On Wed, Aug 12, 2026 at 04:30:37PM +0200, Esben Haabendal wrote:
> In commit 32a5c04d4575 ("iio: accel: mma8452: Use dev_err_probe()") the
> struct device * pointer was assigned to local variable dev, so we can just
> as well reuse that throughout the function for sligthly more readable code.

...

> -		return dev_err_probe(&client->dev, -ENODEV,
> +		return dev_err_probe(dev, -ENODEV,
>  				     "unknown device model\n");

		return dev_err_probe(dev, -ENODEV, "unknown device model\n");

Now a single line.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v4 4/6] iio: accel: mma8452: Support interrupt sharing

[Andy Shevchenko]

On Wed, Aug 12, 2026 at 04:30:35PM +0200, Esben Haabendal wrote:
> Adding handling of rutnime PM suspension in the interrupt handler allows
> sharing interrupt with other devices.
> 
> 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.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v4 6/6] iio: accel: mma8452: Reuse existing dev pointer in mma8452_probe()

[Esben Haabendal]

On Friday, August 14th, 2026 at 10:07, Andy Shevchenko <andriy.shevchenko@intel.com> wrote:

> On Wed, Aug 12, 2026 at 04:30:37PM +0200, Esben Haabendal wrote:
> > In commit 32a5c04d4575 ("iio: accel: mma8452: Use dev_err_probe()") the
> > struct device * pointer was assigned to local variable dev, so we can just
> > as well reuse that throughout the function for sligthly more readable code.
> 
> ...
> 
> > -		return dev_err_probe(&client->dev, -ENODEV,
> > +		return dev_err_probe(dev, -ENODEV,
> >  				     "unknown device model\n");
> 
> 		return dev_err_probe(dev, -ENODEV, "unknown device model\n");
> 
> Now a single line.

Added for v5.

/Esben

Re: [PATCH v4 2/6] iio: accel: mma8452: Optimize struct mm8452_data member orders

[Jonathan Cameron]

On Wed, 12 Aug 2026 16:30:33 +0200
Esben Haabendal <esben@geanix.com> wrote:

> Reorder struct mma8452_data members to avoid holes.
Trivial but sashiko pointed out mm[a]_8452 in the title.
I'll tidy that up if nothing significant comes up.

Interestingly Sashiko also thinks it found a deadlock.
Given you are working with this driver if you have time could
you take a look at that. 

https://sashiko.dev/#/patchset/20260812-mma8452-open-drain-v4-0-bfca15d02b59%40geanix.com

I'm rather surprised to see the lock taken in the runtime
pm suspend callback. It is probably there to close a race
where the device is being suspended and the sampling
frequency is being written.  I'm not immediately sure what
the best way to fix it is. One thing that would work is to
do pm_runtime_get* to raise the reference counter and stop
there being any chance of an autosuspend. 

Jonathan

> 
> Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> Signed-off-by: Esben Haabendal <esben@geanix.com>
> ---
>  drivers/iio/accel/mma8452.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
> index 7d683686dd9d..f645a5c6fd1c 100644
> --- a/drivers/iio/accel/mma8452.c
> +++ b/drivers/iio/accel/mma8452.c
> @@ -106,10 +106,7 @@ struct mma8452_data {
>  	struct i2c_client *client;
>  	struct mutex lock;
>  	struct iio_mount_matrix orientation;
> -	u8 ctrl_reg1;
> -	u8 data_cfg;
>  	const struct mma_chip_info *chip_info;
> -	int sleep_val;
>  	struct regulator *vdd_reg;
>  	struct regulator *vddio_reg;
>  
> @@ -118,6 +115,10 @@ struct mma8452_data {
>  		__be16 channels[3];
>  		aligned_s64 ts;
>  	} buffer;
> +
> +	int sleep_val;
> +	u8 ctrl_reg1;
> +	u8 data_cfg;
>  };
>  
>   /**
> 

Re: [PATCH v4 4/6] iio: accel: mma8452: Support interrupt sharing

[Jonathan Cameron]

On Fri, 14 Aug 2026 11:09:28 +0300
Andy Shevchenko <andriy.shevchenko@intel.com> wrote:

> On Wed, Aug 12, 2026 at 04:30:35PM +0200, Esben Haabendal wrote:
> > Adding handling of rutnime PM suspension in the interrupt handler allows
> > sharing interrupt with other devices.
> > 
> > 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.  
> 
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> 

There are a few sashiko comments on this one. I haven't looked
at them in detail - so if you think they are wrong feel free to say that!

Re: [PATCH v4 2/6] iio: accel: mma8452: Optimize struct mm8452_data member orders

[Esben Haabendal]

"Jonathan Cameron" <jic23@kernel.org> writes:

> On Wed, 12 Aug 2026 16:30:33 +0200
> Esben Haabendal <esben@geanix.com> wrote:
>
>> Reorder struct mma8452_data members to avoid holes.
> Trivial but sashiko pointed out mm[a]_8452 in the title.
> I'll tidy that up if nothing significant comes up.
>
> Interestingly Sashiko also thinks it found a deadlock.
> Given you are working with this driver if you have time could
> you take a look at that.
>
> https://sashiko.dev/#/patchset/20260812-mma8452-open-drain-v4-0-bfca15d02b59%40geanix.com
>
> I'm rather surprised to see the lock taken in the runtime
> pm suspend callback. It is probably there to close a race
> where the device is being suspended and the sampling
> frequency is being written.  I'm not immediately sure what
> the best way to fix it is. One thing that would work is to
> do pm_runtime_get* to raise the reference counter and stop
> there being any chance of an autosuspend.

The mma8452_change_config() function is grabbing &data->lock, and is
forcing chip in stand mode while applying change. This needs to be
synchronized with mma8452_runtime_suspend() switching to standby mode,
to avoid a race condition where mma8452_change_config() would end up
undoing the change made by runtime PM, due to it keeping the old state
in is_active local variable. So far it makes sense.

But I don't see the reason for mma8452_read_raw(IIO_CHAN_INFO_RAW)
grabbing the lock for the call to mma8452_read(). And when
mma8452_trigger_handler() calls mma8452_read() it does so without
data->lock held.

So maybe we we can simply drop the &data->lock from mma8452_read_raw()?

/Esben