[PATCH v2 0/3] io: accel: mma8452: Allow open drain interrupt pin configuration

[PATCH v2 0/3] 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 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 (3):
      dt-bindings: iio: accel: mma8452: Add drive-open-drain
      iio: accel: mma8452: Allow open drain interrupt pin configuration
      iio: accel: mma8452: Optimize struct mm8452_data member orders

 .../devicetree/bindings/iio/accel/fsl,mma8452.yaml |  6 ++++
 drivers/iio/accel/mma8452.c                        | 38 +++++++++++++++++++---
 2 files changed, 40 insertions(+), 4 deletions(-)
---
base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
change-id: 20250401-mma8452-open-drain-81577c41375c

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

[PATCH v2 1/3] 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.

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 v2 2/3] iio: accel: mma8452: Allow open drain interrupt pin configuration

[Esben Haabendal]

When sharing interrupt line with other chips, the interrupt pin most
likely needs to be configured in open-drain mode instead of push-pull.

The PP_OD bit in CTRL_REG3 is set when open-drain mode is configured,
allowing sharing the interrupt line with other devices (with same interrupt
polarity).
The IRQF_SHARED flag is added to request_threaded_irq() flags, indicating
that the interrupt line can be shared with other devices.

Signed-off-by: Esben Haabendal <esben@geanix.com>
---
 drivers/iio/accel/mma8452.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
index 7d683686dd9d..fdf7364d7fed 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
@@ -108,6 +110,7 @@ struct mma8452_data {
 	struct iio_mount_matrix orientation;
 	u8 ctrl_reg1;
 	u8 data_cfg;
+	bool open_drain;
 	const struct mma_chip_info *chip_info;
 	int sleep_val;
 	struct regulator *vdd_reg;
@@ -646,6 +649,22 @@ 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)
 {
@@ -1666,6 +1685,11 @@ static int mma8452_probe(struct i2c_client *client)
 			goto disable_regulators;
 	}
 
+	data->open_drain = device_property_read_bool(&client->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);
 
@@ -1683,7 +1707,8 @@ static int mma8452_probe(struct i2c_client *client)
 
 	if (client->irq) {
 		ret = request_threaded_irq(client->irq, NULL, mma8452_interrupt,
-					   IRQF_TRIGGER_LOW | IRQF_ONESHOT,
+					   IRQF_TRIGGER_LOW | IRQF_ONESHOT |
+					   (data->open_drain ? IRQF_SHARED : 0),
 					   client->name, indio_dev);
 		if (ret)
 			goto buffer_cleanup;
@@ -1800,6 +1825,10 @@ 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 v2 3/3] iio: accel: mma8452: Optimize struct mm8452_data member orders

[Esben Haabendal]

Reorder struct mma8452_data members to avoid holes.

Signed-off-by: Esben Haabendal <esben@geanix.com>
---
 drivers/iio/accel/mma8452.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
index fdf7364d7fed..537263085215 100644
--- a/drivers/iio/accel/mma8452.c
+++ b/drivers/iio/accel/mma8452.c
@@ -108,11 +108,7 @@ struct mma8452_data {
 	struct i2c_client *client;
 	struct mutex lock;
 	struct iio_mount_matrix orientation;
-	u8 ctrl_reg1;
-	u8 data_cfg;
-	bool open_drain;
 	const struct mma_chip_info *chip_info;
-	int sleep_val;
 	struct regulator *vdd_reg;
 	struct regulator *vddio_reg;
 
@@ -121,6 +117,11 @@ struct mma8452_data {
 		__be16 channels[3];
 		aligned_s64 ts;
 	} buffer;
+
+	int sleep_val;
+	u8 ctrl_reg1;
+	u8 data_cfg;
+	bool open_drain;
 };
 
  /**

-- 
2.55.0

Re: [PATCH v2 2/3] iio: accel: mma8452: Allow open drain interrupt pin configuration

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

New issues:
- [High] Adding IRQF_SHARED allows the interrupt handler to be invoked by other devices sharing the same IRQ line, even when the MMA8452 is runtime-suspended. The interrupt handler unconditionally performs an I2C read, which causes bus errors when the device is unpowered.

Pre-existing issues:
- [High] Device configuration state is lost on runtime suspend and never restored on resume, leading to silent scale corruption and loss of interrupts.
--

--- Patch [2]: [PATCH v2 2/3] iio: accel: mma8452: Allow open drain interrupt pin configuration ---
commit 066cff55fa993aded66754d740665ed28050f829
Author: Esben Haabendal <esben@geanix.com>

iio: accel: mma8452: Allow open drain interrupt pin configuration

This patch allows configuring the interrupt pin in open-drain mode by setting
the PP_OD bit in CTRL_REG3 based on the "drive-open-drain" device property.
It also adds the IRQF_SHARED flag to request_threaded_irq() when open-drain
is enabled, allowing the interrupt line to be shared with other devices.

> diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
> index 7d683686dd9d6..fdf7364d7fede 100644
> --- a/drivers/iio/accel/mma8452.c
> +++ b/drivers/iio/accel/mma8452.c
[ ... ]
> @@ -1683,7 +1707,8 @@ static int mma8452_probe(struct i2c_client *client)
>  
>  	if (client->irq) {
>  		ret = request_threaded_irq(client->irq, NULL, mma8452_interrupt,
> -					   IRQF_TRIGGER_LOW | IRQF_ONESHOT,
> +					   IRQF_TRIGGER_LOW | IRQF_ONESHOT |
> +					   (data->open_drain ? IRQF_SHARED : 0),

[Severity: High]
With the addition of IRQF_SHARED here, could the interrupt handler be invoked
by other devices sharing the line while the MMA8452 is runtime-suspended?

Looking at mma8452_interrupt(), it unconditionally performs an I2C read:

mma8452_interrupt()
{
	src = i2c_smbus_read_byte_data(data->client, MMA8452_INT_SRC);
	if (src < 0)
		return IRQ_NONE;
...
}

If the MMA8452 goes into runtime suspend (cutting power to the sensor) and
another device triggers the shared interrupt line, wouldn't this unconditional
I2C read attempt to access an unpowered device, leading to I2C bus timeouts or
NACK errors?

>  					   client->name, indio_dev);
>  		if (ret)
>  			goto buffer_cleanup;
[ ... ]
> @@ -1800,6 +1825,10 @@ static int mma8452_runtime_resume(struct device *dev)
>  		return ret;
>  	}
>  
> +	ret = mma8452_set_interrupt_pin_mode(data);

[Severity: High]
This is a pre-existing issue, but I noticed it while looking at the resume
path. Are we losing device configuration state across runtime suspend?

The mma8452_runtime_suspend() function disables vdd_reg and vddio_reg,
cutting power and resetting registers to their Power-On-Reset defaults.
When mma8452_runtime_resume() is called, it only restores CTRL_REG1 (via
mma8452_active) and now CTRL_REG3.

Does this leave other configurations unrestored? For example, MMA8452_DATA_CFG
defaults back to 2G while the software cache retains user configurations, and
MMA8452_CTRL_REG4 and MMA8452_CTRL_REG5 lose their event interrupt routings.
Couldn't this cause corrupted scale calculations or lost interrupts after the
device's first idle suspend period?

> +	if (ret)
> +		goto runtime_resume_failed;
> +
>  	ret = mma8452_active(data);
>  	if (ret < 0)
>  		goto runtime_resume_failed;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260715-mma8452-open-drain-v2-0-95be9f5f4795@geanix.com?part=2

Re: [PATCH v2 3/3] iio: accel: mma8452: Optimize struct mm8452_data member orders

[Joshua Crofts]

On Wed, 15 Jul 2026 14:33:29 +0200
Esben Haabendal <esben@geanix.com> wrote:

> Reorder struct mma8452_data members to avoid holes.
> 
> Signed-off-by: Esben Haabendal <esben@geanix.com>
> ---
>  drivers/iio/accel/mma8452.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
> index fdf7364d7fed..537263085215 100644
> --- a/drivers/iio/accel/mma8452.c
> +++ b/drivers/iio/accel/mma8452.c
> @@ -108,11 +108,7 @@ struct mma8452_data {
>  	struct i2c_client *client;
>  	struct mutex lock;
>  	struct iio_mount_matrix orientation;
> -	u8 ctrl_reg1;
> -	u8 data_cfg;
> -	bool open_drain;
>  	const struct mma_chip_info *chip_info;
> -	int sleep_val;
>  	struct regulator *vdd_reg;
>  	struct regulator *vddio_reg;
>  
> @@ -121,6 +117,11 @@ struct mma8452_data {
>  		__be16 channels[3];
>  		aligned_s64 ts;
>  	} buffer;
> +
> +	int sleep_val;
> +	u8 ctrl_reg1;
> +	u8 data_cfg;
> +	bool open_drain;
>  };
>  
>   /**
> 

LGTM.

Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>

-- 
Kind regards

CJD

Re: [PATCH v2 3/3] iio: accel: mma8452: Optimize struct mm8452_data member orders

[Joshua Crofts]

On Wed, 15 Jul 2026 14:33:29 +0200
Esben Haabendal <esben@geanix.com> wrote:

> Reorder struct mma8452_data members to avoid holes.
> 
> Signed-off-by: Esben Haabendal <esben@geanix.com>
> ---
>  drivers/iio/accel/mma8452.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
> index fdf7364d7fed..537263085215 100644
> --- a/drivers/iio/accel/mma8452.c
> +++ b/drivers/iio/accel/mma8452.c
> @@ -108,11 +108,7 @@ struct mma8452_data {
>  	struct i2c_client *client;
>  	struct mutex lock;
>  	struct iio_mount_matrix orientation;
> -	u8 ctrl_reg1;
> -	u8 data_cfg;
> -	bool open_drain;
>  	const struct mma_chip_info *chip_info;
> -	int sleep_val;
>  	struct regulator *vdd_reg;
>  	struct regulator *vddio_reg;
>  
> @@ -121,6 +117,11 @@ struct mma8452_data {
>  		__be16 channels[3];
>  		aligned_s64 ts;
>  	} buffer;
> +
> +	int sleep_val;
> +	u8 ctrl_reg1;
> +	u8 data_cfg;
> +	bool open_drain;
>  };

Also quick thing, in order to prevent too much cruft, could you
please move this patch before patch 2? You introduce the bool in
2 and then move it to the end in 3, better for you to reorder it
first and add the bool after, otherwise you get these "ping-pong"
style changes (Andy's words). My reviewed-by still stands either way,
so feel free to add it once reordered.

-- 
Kind regards

CJD

Re: [PATCH v2 0/3] io: accel: mma8452: Allow open drain interrupt pin configuration

[Andy Shevchenko]

On Wed, Jul 15, 2026 at 02:33:26PM +0200, Esben Haabendal wrote:
> 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.

NAK.

Please, do not send a new version until everything is settled down in the
previous round. Let's continue discussion in v1.

-- 
With Best Regards,
Andy Shevchenko