Date:   Fri, 27 Oct 2023 06:14:58 +0000
From:   Thomas Weißschuh <linux@...ssschuh.net>
To:     Anshul Dalal <anshulusr@...il.com>
Cc:     linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jeff LaBundy <jeff@...undy.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/2] input: joystick: driver for Adafruit Seesaw
 Gamepad

Hi Anshul,

thanks for the reworks!

Some more comments inline.

On 2023-10-27 10:48:11+0530, Anshul Dalal wrote:
> Adds a driver for a mini gamepad that communicates over i2c, the gamepad
> has bidirectional thumb stick input and six buttons.
> 
> The gamepad chip utilizes the open framework from Adafruit called 'Seesaw'
> to transmit the ADC data for the joystick and digital pin state for the
> buttons. I have only implemented the functionality required to receive the
> thumb stick and button state.
> 
> Steps in reading the gamepad state over i2c:
>   1. Reset the registers
>   2. Set the pin mode of the pins specified by the `BUTTON_MASK` to input
>       `BUTTON_MASK`: A bit-map for the six digital pins internally
>        connected to the joystick buttons.
>   3. Enable internal pullup resistors for the `BUTTON_MASK`
>   4. Bulk set the pin state HIGH for `BUTTON_MASK`
>   5. Poll the device for button and joystick state done by:
>       `seesaw_read_data(struct i2c_client *client, struct seesaw_data *data)`
> 
> Product page:
>   https://www.adafruit.com/product/5743
> Arduino driver:
>   https://github.com/adafruit/Adafruit_Seesaw
> 
> Driver tested on RPi Zero 2W
> 
> Reviewed-by: Thomas Weißschuh <linux@...ssschuh.net>
> Signed-off-by: Anshul Dalal <anshulusr@...il.com>
> ---
> Changes for v6:
> - Added TODO
> - Removed `clang-format` directives
> - Namespaced device buttons
> - Removed `char physical_path[32]` field from `struct seesaw_gamepad`
> - Added `packed` attribute to `struct seesaw_data`
> - Moved from having booleans per button to single `u32 button_state`
> - Added `seesaw_button_description` array to directly associate device
>   buttons with respective keycodes
> - Added wrapper functions `seesaw_register_` around `i2c_master_` API
> - Ratelimited input error reporting with `dev_err_ratelimited`
> - Removed `of_device_id`
> 
> Changes for v5:
> - Added link to the datasheet
> - Added debug log message when `seesaw_read_data` fails
> 
> Changes for v4:
> - Changed `1UL << BUTTON_` to BIT(BUTTON_)
> - Removed `hardware_id` field from `struct seesaw_gamepad`
> - Removed redundant checks for the number of bytes written and received by
>   `i2c_master_send` and `i2c_master_recv`
> - Used `get_unaligned_be32` to instantiate `u32 result` from `read_buf`
> - Changed  `result & (1UL << BUTTON_)` to
>   `test_bit(BUTTON_, (long *)&result)`
> - Changed `KBUILD_MODNAME` in id-tables to `SEESAW_DEVICE_NAME`
> - Fixed formatting issues
> - Changed button reporting:
>     Since the gamepad had the action buttons in a non-standard layout:
>          (X)
>       (Y)   (A)
>          (B)
>     Therefore moved to using generic directional action button event codes
>     instead of BTN_[ABXY].
> 
> Changes for v3:
> - no updates
> 
> Changes for v2:
> adafruit-seesaw.c:
> - Renamed file from 'adafruit_seesaw.c'
> - Changed device name from 'seesaw_gamepad' to 'seesaw-gamepad'
> - Changed count parameter for receiving joystick x on line 118:
>     `2` to `sizeof(write_buf)`
> - Fixed invalid buffer size on line 123 and 126:
>     `data->y` to `sizeof(data->y)`
> - Added comment for the `mdelay(10)` on line 169
> - Changed inconsistent indentation on line 271
> Kconfig:
> - Fixed indentation for the help text
> - Updated module name
> Makefile:
> - Updated module object file name
> MAINTAINERS:
> - Updated file name for the driver and bindings
> 
>  MAINTAINERS                              |   7 +
>  drivers/input/joystick/Kconfig           |   9 +
>  drivers/input/joystick/Makefile          |   1 +
>  drivers/input/joystick/adafruit-seesaw.c | 310 +++++++++++++++++++++++
>  4 files changed, 327 insertions(+)
>  create mode 100644 drivers/input/joystick/adafruit-seesaw.c

[..]

> diff --git a/drivers/input/joystick/adafruit-seesaw.c b/drivers/input/joystick/adafruit-seesaw.c
> new file mode 100644
> index 000000000000..1aa6fbe4fda4
> --- /dev/null
> +++ b/drivers/input/joystick/adafruit-seesaw.c
> @@ -0,0 +1,310 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2023 Anshul Dalal <anshulusr@...il.com>
> + *
> + * Driver for Adafruit Mini I2C Gamepad
> + *
> + * Based on the work of:
> + *	Oleh Kravchenko (Sparkfun Qwiic Joystick driver)
> + *
> + * Datasheet: https://cdn-learn.adafruit.com/downloads/pdf/gamepad-qt.pdf
> + * Product page: https://www.adafruit.com/product/5743
> + * Firmware and hardware sources: https://github.com/adafruit/Adafruit_Seesaw
> + *
> + * TODO:
> + *	- Add interrupt support
> + */
> +
> +#include <asm-generic/unaligned.h>
> +#include <linux/bits.h>
> +#include <linux/delay.h>
> +#include <linux/i2c.h>
> +#include <linux/input.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +
> +#define SEESAW_DEVICE_NAME	"seesaw-gamepad"
> +
> +#define SEESAW_STATUS_BASE	0
> +#define SEESAW_GPIO_BASE	1
> +#define SEESAW_ADC_BASE		9
> +
> +#define SEESAW_GPIO_DIRCLR_BULK	3
> +#define SEESAW_GPIO_BULK	4
> +#define SEESAW_GPIO_BULK_SET	5
> +#define SEESAW_GPIO_PULLENSET	11
> +
> +#define SEESAW_STATUS_HW_ID	1
> +#define SEESAW_STATUS_SWRST	127
> +
> +#define SEESAW_ADC_OFFSET	7
> +
> +#define SEESAW_BUTTON_A		5
> +#define SEESAW_BUTTON_B		1
> +#define SEESAW_BUTTON_X		6
> +#define SEESAW_BUTTON_Y		2
> +#define SEESAW_BUTTON_START	16
> +#define SEESAW_BUTTON_SELECT	0
> +
> +#define SEESAW_ANALOG_X		14
> +#define SEESAW_ANALOG_Y		15
> +
> +#define SEESAW_JOYSTICK_MAX_AXIS	1023
> +#define SEESAW_JOYSTICK_FUZZ		2
> +#define SEESAW_JOYSTICK_FLAT		4
> +
> +#define SEESAW_GAMEPAD_POLL_INTERVAL	16
> +#define SEESAW_GAMEPAD_POLL_MIN		8
> +#define SEESAW_GAMEPAD_POLL_MAX		32
> +
> +u32 SEESAW_BUTTON_MASK = BIT(SEESAW_BUTTON_A) | BIT(SEESAW_BUTTON_B) |
> +			 BIT(SEESAW_BUTTON_X) | BIT(SEESAW_BUTTON_Y) |
> +			 BIT(SEESAW_BUTTON_START) | BIT(SEESAW_BUTTON_SELECT);
> +
> +struct seesaw_gamepad {
> +	struct input_dev *input_dev;
> +	struct i2c_client *i2c_client;
> +};
> +
> +struct seesaw_data {
> +	__be16 x;
> +	__be16 y;

The fact that these are big endian is now an implementation detail
hidden within seesaw_read_data(), so the __be16 can go away.

> +	u32 button_state;
> +} __packed;

While this was requested by Jeff I don't think it's correct.
The struct is never received in this form from the device.
I guess he also got confused, like me, by the fact that data is directly
read into the fields of the struct.

See my comment seesaw_read_data().

> +struct seesaw_button_description {
> +	unsigned int code;
> +	unsigned int bit;
> +};
> +
> +static const struct seesaw_button_description seesaw_buttons[] = {
> +	{
> +		.code = BTN_EAST,
> +		.bit = SEESAW_BUTTON_A,
> +	},
> +	{
> +		.code = BTN_SOUTH,
> +		.bit = SEESAW_BUTTON_B,
> +	},
> +	{
> +		.code = BTN_NORTH,
> +		.bit = SEESAW_BUTTON_X,
> +	},
> +	{
> +		.code = BTN_WEST,
> +		.bit = SEESAW_BUTTON_Y,
> +	},
> +	{
> +		.code = BTN_START,
> +		.bit = SEESAW_BUTTON_START,
> +	},
> +	{
> +		.code = BTN_SELECT,
> +		.bit = SEESAW_BUTTON_SELECT,
> +	},
> +};

This looks very much like a sparse keymap which can be implemented with
the helpers from <linux/input/sparse-keymap.h>.

Personally I prefer each keymap entry to be on a single line (without
designated initializers, maybe with some alignment) to save a bunch of
vertical space.

> +
> +static int seesaw_register_read(struct i2c_client *client, u8 register_high,
> +				u8 register_low, char *buf, int count)
> +{
> +	int ret;
> +	u8 register_buf[2] = { register_high, register_low };
> +
> +	ret = i2c_master_send(client, register_buf, sizeof(register_buf));
> +	if (ret < 0)
> +		return ret;
> +	ret = i2c_master_recv(client, buf, count);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static int seesaw_register_write_u8(struct i2c_client *client, u8 register_high,
> +				    u8 register_low, u8 value)
> +{
> +	int ret;
> +	u8 write_buf[3] = { register_high, register_low, value };
> +
> +	ret = i2c_master_send(client, write_buf, sizeof(write_buf));
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static int seesaw_register_write_u32(struct i2c_client *client,
> +				     u8 register_high, u8 register_low,
> +				     u32 value)
> +{
> +	int ret;
> +	u8 write_buf[6] = { register_high, register_low };
> +
> +	put_unaligned_be32(value, write_buf + 2);
> +	ret = i2c_master_send(client, write_buf, sizeof(write_buf));
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static int seesaw_read_data(struct i2c_client *client, struct seesaw_data *data)
> +{
> +	int ret;
> +	u8 read_buf[4];
> +
> +	ret = seesaw_register_read(client, SEESAW_GPIO_BASE, SEESAW_GPIO_BULK,
> +				   read_buf, sizeof(read_buf));
> +	if (ret)
> +		return ret;
> +
> +	data->button_state = ~get_unaligned_be32(&read_buf);
> +
> +	ret = seesaw_register_read(client, SEESAW_ADC_BASE,
> +				   SEESAW_ADC_OFFSET + SEESAW_ANALOG_X,
> +				   (char *)&data->x, sizeof(data->x));

Nitpick: read into a dedicated local variable instead of 'data', as it's
easier to understand.

> +	if (ret)
> +		return ret;
> +	/*
> +	 * ADC reads left as max and right as 0, must be reversed since kernel
> +	 * expects reports in opposite order.
> +	 */
> +	data->x = SEESAW_JOYSTICK_MAX_AXIS - be16_to_cpu(data->x);
> +
> +	ret = seesaw_register_read(client, SEESAW_ADC_BASE,
> +				   SEESAW_ADC_OFFSET + SEESAW_ANALOG_Y,
> +				   (char *)&data->y, sizeof(data->y));
> +	if (ret)
> +		return ret;
> +	data->y = be16_to_cpu(data->y);
> +
> +	return 0;
> +}
> +
> +static void seesaw_poll(struct input_dev *input)
> +{
> +	int err, i;
> +	struct seesaw_gamepad *private = input_get_drvdata(input);
> +	struct seesaw_data data;
> +
> +	err = seesaw_read_data(private->i2c_client, &data);
> +	if (err != 0) {

Everywhere else this is just 'if (err)'.

> +		dev_err_ratelimited(&input->dev,
> +				    "failed to read joystick state: %d\n", err);
> +		return;
> +	}
> +
> +	input_report_abs(input, ABS_X, data.x);
> +	input_report_abs(input, ABS_Y, data.y);
> +
> +	for (i = 0; i < ARRAY_SIZE(seesaw_buttons); i++) {
> +		input_report_key(input, seesaw_buttons[i].code,
> +				 data.button_state &
> +					 BIT(seesaw_buttons[i].bit));
> +	}
> +	input_sync(input);
> +}
> +
> +static int seesaw_probe(struct i2c_client *client)
> +{
> +	int err, i;
> +	u8 hardware_id;
> +	struct seesaw_gamepad *seesaw;
> +
> +	err = seesaw_register_write_u8(client, SEESAW_STATUS_BASE,
> +				       SEESAW_STATUS_SWRST, 0xFF);
> +	if (err)
> +		return err;
> +
> +	/* Wait for the registers to reset before proceeding */
> +	mdelay(10);
> +
> +	seesaw = devm_kzalloc(&client->dev, sizeof(*seesaw), GFP_KERNEL);
> +	if (!seesaw)
> +		return -ENOMEM;
> +
> +	err = seesaw_register_read(client, SEESAW_STATUS_BASE,
> +				   SEESAW_STATUS_HW_ID, &hardware_id, 1);
> +	if (err)
> +		return err;
> +
> +	dev_dbg(&client->dev, "Adafruit Seesaw Gamepad, Hardware ID: %02x\n",
> +		hardware_id);
> +
> +	/* Set Pin Mode to input and enable pull-up resistors */
> +	err = seesaw_register_write_u32(client, SEESAW_GPIO_BASE,
> +					SEESAW_GPIO_DIRCLR_BULK,
> +					SEESAW_BUTTON_MASK);
> +	if (err)
> +		return err;
> +	err = seesaw_register_write_u32(client, SEESAW_GPIO_BASE,
> +					SEESAW_GPIO_PULLENSET,
> +					SEESAW_BUTTON_MASK);
> +	if (err)
> +		return err;
> +	err = seesaw_register_write_u32(client, SEESAW_GPIO_BASE,
> +					SEESAW_GPIO_BULK_SET,
> +					SEESAW_BUTTON_MASK);
> +	if (err)
> +		return err;
> +
> +	seesaw->i2c_client = client;
> +	i2c_set_clientdata(client, seesaw);

I'm not familiar with the i2c APIs but this clientdata seems to be
unused.

> +
> +	seesaw->input_dev = devm_input_allocate_device(&client->dev);
> +	if (!seesaw->input_dev)
> +		return -ENOMEM;
> +
> +	seesaw->input_dev->id.bustype = BUS_I2C;
> +	seesaw->input_dev->name = "Adafruit Seesaw Gamepad";
> +	seesaw->input_dev->phys = "i2c/" SEESAW_DEVICE_NAME;
> +	input_set_drvdata(seesaw->input_dev, seesaw);
> +	input_set_abs_params(seesaw->input_dev, ABS_X, 0,
> +			     SEESAW_JOYSTICK_MAX_AXIS, SEESAW_JOYSTICK_FUZZ,
> +			     SEESAW_JOYSTICK_FLAT);
> +	input_set_abs_params(seesaw->input_dev, ABS_Y, 0,
> +			     SEESAW_JOYSTICK_MAX_AXIS, SEESAW_JOYSTICK_FUZZ,
> +			     SEESAW_JOYSTICK_FLAT);
> +	for (i = 0; i < ARRAY_SIZE(seesaw_buttons); i++) {
> +		input_set_capability(seesaw->input_dev, EV_KEY,
> +				     seesaw_buttons[i].code);
> +	}
> +
> +	err = input_setup_polling(seesaw->input_dev, seesaw_poll);
> +	if (err) {
> +		dev_err(&client->dev, "failed to set up polling: %d\n", err);
> +		return err;
> +	}
> +
> +	input_set_poll_interval(seesaw->input_dev,
> +				SEESAW_GAMEPAD_POLL_INTERVAL);

Why the linebreak on this line and not on the ones below?

> +	input_set_max_poll_interval(seesaw->input_dev, SEESAW_GAMEPAD_POLL_MAX);
> +	input_set_min_poll_interval(seesaw->input_dev, SEESAW_GAMEPAD_POLL_MIN);
> +
> +	err = input_register_device(seesaw->input_dev);
> +	if (err) {
> +		dev_err(&client->dev, "failed to register joystick: %d\n", err);
> +		return err;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct i2c_device_id seesaw_id_table[] = {
> +	{ SEESAW_DEVICE_NAME, 0 },
> +	{ /* Sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(i2c, seesaw_id_table);
> +
> +static struct i2c_driver seesaw_driver = {
> +	.driver = {
> +		.name = SEESAW_DEVICE_NAME,
> +	},
> +	.id_table = seesaw_id_table,
> +	.probe = seesaw_probe,
> +};
> +module_i2c_driver(seesaw_driver);
> +
> +MODULE_AUTHOR("Anshul Dalal <anshulusr@...il.com>");
> +MODULE_DESCRIPTION("Adafruit Mini I2C Gamepad driver");
> +MODULE_LICENSE("GPL");
> -- 
> 2.42.0
> 

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