Re: [PATCH] input: add SparkFun Qwiic Joystick driver

[Jeff LaBundy <jeff@labundy.com>]

Hi Oleh,

Neat little device; some comments below.

On Mon, May 31, 2021 at 04:32:43PM +0300, Oleh Kravchenko wrote:
> A simple analog joystick built on Low Power ATtiny85 Microcontroller.
> Directional movements are measured with two 10 kΩ potentiometers
> connected with a gimbal mechanism that separates the horizontal and
> vertical movements. This joystick also has a select button that is actuated
> when the joystick is pressed down.
> 
> Input events polled over the I2C bus.
> 
> Product page:
> https://www.sparkfun.com/products/15168
> Firmware and hardware sources:
> https://github.com/sparkfun/Qwiic_Joystick
> 
> Tested on RPi4B and O4-iMX-NANO boards.
> 
> Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> Cc: Device Tree mailing list <devicetree@vger.kernel.org>
> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> Cc: Jiri Kosina <jikos@jikos.cz>
> Cc: Patchwork Bot <patchwork-bot@kernel.org>
> Signed-off-by: Oleh Kravchenko <oleg@kaa.org.ua>
> ---

Please use a version number (e.g. v2, v3) and add a change log under
the '---' when sending new versions.

>  .../bindings/input/qwiic-joystick.yaml        |  31 ++++
>  .../devicetree/bindings/vendor-prefixes.yaml  |   2 +
>  drivers/input/joystick/Kconfig                |   9 +
>  drivers/input/joystick/Makefile               |   1 +
>  drivers/input/joystick/qwiic-joystick.c       | 169 ++++++++++++++++++
>  5 files changed, 212 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/input/qwiic-joystick.yaml
>  create mode 100644 drivers/input/joystick/qwiic-joystick.c

Bindings must be a separate patch with Rob Herring (see MAINTAINERS)
on the To: list.

> 
> diff --git a/Documentation/devicetree/bindings/input/qwiic-joystick.yaml b/Documentation/devicetree/bindings/input/qwiic-joystick.yaml
> new file mode 100644
> index 000000000000..51cadeb350f2
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/input/qwiic-joystick.yaml
> @@ -0,0 +1,31 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +# Copyright 2021 Oleh Kravchenko
> +%YAML 1.2
> +---
> +$id: "http://devicetree.org/schemas/input/qwiic-joystick.yaml#"
> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
> +
> +title: SparkFun Qwiic Joystick
> +
> +maintainers:
> +  - Oleh Kravchenko <oleg@kaa.org.ua>
> +
> +description: |
> +  Bindings for SparkFun Qwiic Joystick (COM-15168).
> +  https://www.sparkfun.com/products/15168
> +
> +properties:
> +  compatible:
> +    const: sparkfun,qwiic-joystick
> +
> +required:
> +  - compatible

'reg' is required as well.

> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    qwiic@20 {
> +        compatible = "sparkfun,qwiic-joystick";
> +        reg = <0x20>;
> +    };
> diff --git a/Documentation/devicetree/bindings/vendor-prefixes.yaml b/Documentation/devicetree/bindings/vendor-prefixes.yaml
> index 944b02bb96d7..a5631e68f5d1 100644
> --- a/Documentation/devicetree/bindings/vendor-prefixes.yaml
> +++ b/Documentation/devicetree/bindings/vendor-prefixes.yaml
> @@ -1060,6 +1060,8 @@ patternProperties:
>      description: Sony Corporation
>    "^spansion,.*":
>      description: Spansion Inc.
> +  "^sparkfun,.*":
> +    description: SparkFun Electronics
>    "^sprd,.*":
>      description: Spreadtrum Communications Inc.
>    "^sst,.*":
> diff --git a/drivers/input/joystick/Kconfig b/drivers/input/joystick/Kconfig
> index 5e38899058c1..7dfe8ea90923 100644
> --- a/drivers/input/joystick/Kconfig
> +++ b/drivers/input/joystick/Kconfig
> @@ -372,6 +372,15 @@ config JOYSTICK_PXRC
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called pxrc.
>  
> +config JOYSTICK_QWIIC
> +	tristate "SparkFun Qwiic Joystick"
> +	depends on I2C
> +	help
> +	  Say Y here if you want to use the SparkFun Qwiic Joystick.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called qwiic-joystick.
> +
>  config JOYSTICK_FSIA6B
>  	tristate "FlySky FS-iA6B RC Receiver"
>  	select SERIO
> diff --git a/drivers/input/joystick/Makefile b/drivers/input/joystick/Makefile
> index 31d720c9e493..5174b8aba2dd 100644
> --- a/drivers/input/joystick/Makefile
> +++ b/drivers/input/joystick/Makefile
> @@ -27,6 +27,7 @@ obj-$(CONFIG_JOYSTICK_MAPLE)		+= maplecontrol.o
>  obj-$(CONFIG_JOYSTICK_N64)		+= n64joy.o
>  obj-$(CONFIG_JOYSTICK_PSXPAD_SPI)	+= psxpad-spi.o
>  obj-$(CONFIG_JOYSTICK_PXRC)		+= pxrc.o
> +obj-$(CONFIG_JOYSTICK_QWIIC)		+= qwiic-joystick.o
>  obj-$(CONFIG_JOYSTICK_SIDEWINDER)	+= sidewinder.o
>  obj-$(CONFIG_JOYSTICK_SPACEBALL)	+= spaceball.o
>  obj-$(CONFIG_JOYSTICK_SPACEORB)		+= spaceorb.o
> diff --git a/drivers/input/joystick/qwiic-joystick.c b/drivers/input/joystick/qwiic-joystick.c
> new file mode 100644
> index 000000000000..9b7ab0dd1218
> --- /dev/null
> +++ b/drivers/input/joystick/qwiic-joystick.c
> @@ -0,0 +1,169 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2021 Oleh Kravchenko <oleg@kaa.org.ua>
> +
> +/*
> + * SparkFun Qwiic Joystick
> + * Product page:https://www.sparkfun.com/products/15168
> + * Firmware and hardware sources:https://github.com/sparkfun/Qwiic_Joystick
> + */

Nit: typically the copyright information goes in the multi-line introductory
comments; there is no need for a newline after the SPDX identifier either.

> +
> +#include <linux/bits.h>
> +#include <linux/i2c.h>
> +#include <linux/input.h>
> +#include <linux/module.h>
> +
> +#define QWIIC_JSK_REG_VERS	0
> +#define QWIIC_JSK_REG_DATA	3
> +
> +#define QWIIC_JSK_MAX_AXIS	GENMASK(10, 0)
> +#define QWIIC_JSK_FUZZ		2
> +#define QWIIC_JSK_FLAT		2
> +
> +struct qwiic_jsk {
> +	char			phys[32];
> +	struct input_dev	*dev;
> +	struct i2c_client	*i2c;
> +};
> +
> +struct qwiic_ver {
> +	u8 addr;
> +	u8 major;
> +	u8 minor;
> +} __packed;
> +
> +struct qwiic_data {
> +	u8 hx;
> +	u8 lx;
> +	u8 hy;
> +	u8 ly;
> +	u8 thumb;
> +} __packed;

Let's use __be16 for 16-bit big-endian horizontal and vertical position.

> +
> +static void qwiic_poll(struct input_dev *input)
> +{
> +	struct qwiic_jsk	*priv;
> +	struct qwiic_data	data;
> +	int			ret;
> +	int			x, y, btn;

No need to align these declarations.

> +
> +	priv = input_get_drvdata(input);
> +
> +	ret = i2c_smbus_read_i2c_block_data(priv->i2c, QWIIC_JSK_REG_DATA,
> +					    sizeof(data), (u8 *)&data);
> +	if (ret == sizeof(data)) {

This is personal preference, but returning early on error avoids having
to indent the rest of the function.

> +		x = (data.hx << 8 | data.lx) >> 6;
> +		y = (data.hy << 8 | data.ly) >> 6;

With hx/lx and hy/ly defined using __be16, you can use be16_to_cpu() to
resolve the 16-bit value. A comment to explain the 6-bit shift from the
documentation would be useful too.

> +		btn = !!!data.thumb;

I don't think the triple-not is necessary as input_report_key() already
squashes non-zero values to 1 with '!!'. If register 0x07's polarity is
inverted, just pass !data.thumb to input_report_key().

> +
> +		input_report_abs(input, ABS_X, x);
> +		input_report_abs(input, ABS_Y, y);
> +		input_report_key(input, BTN_THUMBL, btn);
> +
> +		input_sync(input);
> +	}
> +}
> +
> +static int qwiic_probe(struct i2c_client *i2c, const struct i2c_device_id *id)

It's much more common (and easier to read) if the i2c_client struct is
passed as *client.

> +{
> +	struct qwiic_jsk	*priv;
> +	struct qwiic_ver	vers;
> +	int			ret;

No need to align these declarations.

> +
> +	ret = i2c_smbus_read_i2c_block_data(i2c, QWIIC_JSK_REG_VERS,
> +					    sizeof(vers), (u8 *)&vers);
> +	if (ret != sizeof(vers)) {
> +		ret = -EIO;
> +		goto err;
> +	}

If i2c_smbus_read_i2c_block_data() returned a negative value, the original
return value should be preserved. Only return -EIO if 0 <= ret < sizeof().

You can also simply return directly; there is nothing to be undone at this
stage.

> +
> +	if (i2c->addr != vers.addr) {
> +		dev_err(&i2c->dev, "address doesn't match!\n");
> +		ret = -ENODEV;
> +		goto err;
> +	}

This error should be impossible. If the address in dts does not match what
the hardware is expecting, i2c_smbus_read_i2c_block_data() would have been
NAK'd in the first place.

> +
> +	dev_info(&i2c->dev, "SparkFun Qwiic Joystick, FW: %d.%d\n",
> +		 vers.major, vers.minor);

This should be dev_dbg() at most.

> +
> +	priv = devm_kzalloc(&i2c->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}

Just return -ENOMEM here.

> +
> +	priv->i2c = i2c;
> +	snprintf(priv->phys, sizeof(priv->phys), "i2c/%s", dev_name(&i2c->dev));
> +	i2c_set_clientdata(i2c, priv);
> +
> +	priv->dev = devm_input_allocate_device(&i2c->dev);
> +	if (!priv->dev) {
> +		dev_err(&i2c->dev, "failed to allocate input device\n");

No need for a print here.

> +		ret = -ENOMEM;
> +		goto err;

Just return -ENOMEM here.

> +	}
> +
> +	priv->dev->dev.parent = &i2c->dev;

This is not necessary; devm_input_allocate_device() takes care of it.

> +	priv->dev->id.bustype = BUS_I2C;
> +	priv->dev->name = "SparkFun Qwiic Joystick";
> +	priv->dev->phys = priv->phys;
> +	input_set_drvdata(priv->dev, priv);
> +
> +	input_set_abs_params(priv->dev, ABS_X, 0, QWIIC_JSK_MAX_AXIS,
> +			     QWIIC_JSK_FUZZ, QWIIC_JSK_FLAT);
> +	input_set_abs_params(priv->dev, ABS_Y, 0, QWIIC_JSK_MAX_AXIS,
> +			     QWIIC_JSK_FUZZ, QWIIC_JSK_FLAT);
> +	input_set_capability(priv->dev, EV_KEY, BTN_THUMBL);
> +
> +	ret = input_setup_polling(priv->dev, qwiic_poll);
> +	if (ret) {
> +		dev_err(&i2c->dev, "failed to set up polling: %d\n", ret);
> +		goto err;
> +	}

Again, you can just return 'ret' here.

> +	input_set_poll_interval(priv->dev, 16);
> +	input_set_min_poll_interval(priv->dev, 8);
> +	input_set_max_poll_interval(priv->dev, 32);

Is there any reason not to #define these intervals?

> +
> +	ret = input_register_device(priv->dev);
> +	if (ret)
> +		dev_err(&i2c->dev, "failed to register joystick: %d\n", ret);
> +
> +err:

This goto label is unnecessary.

> +	return ret;
> +}
> +
> +static int qwiic_remove(struct i2c_client *i2c)
> +{
> +	struct qwiic_jsk *priv;
> +
> +	priv = i2c_get_clientdata(i2c);
> +	input_unregister_device(priv->dev);
> +
> +	return 0;
> +}

Because the input device was created with devm_input_allocate_device(),
input_register_device() is managed as well. Therefore you can drop the
remove callback altogether.

> +
> +static const struct of_device_id of_qwiic_match[] = {
> +	{ .compatible = "sparkfun,qwiic-joystick", },
> +	{},

Nit: { }

> +};
> +MODULE_DEVICE_TABLE(of, of_qwiic_match);
> +
> +static const struct i2c_device_id qwiic_id_table[] = {
> +	{ KBUILD_MODNAME, 0 },
> +	{},

And here (see other drivers).

> +};
> +MODULE_DEVICE_TABLE(i2c, qwiic_id_table);
> +
> +static struct i2c_driver qwiic_driver = {
> +	.driver = {
> +		.name		= KBUILD_MODNAME,
> +		.of_match_table	= of_match_ptr(of_qwiic_match),
> +	},
> +	.id_table	= qwiic_id_table,
> +	.probe		= qwiic_probe,
> +	.remove		= qwiic_remove,
> +};
> +module_i2c_driver(qwiic_driver);

No need for alignment here either.

> +
> +MODULE_AUTHOR("Oleh Kravchenko <oleg@kaa.org.ua>");
> +MODULE_DESCRIPTION("SparkFun Qwiic Joystick driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.26.3
> 

Kind regards,
Jeff LaBundy