Message-ID: <20231020120310.vrn6ew3fcg5e545w@pengutronix.de>
Date:   Fri, 20 Oct 2023 14:03:10 +0200
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     Kamel Bouhara <kamel.bouhara@...tlin.com>
Cc:     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>,
        Henrik Rydberg <rydberg@...math.org>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, mark.satterthwaite@...chnetix.com,
        bartp@...sheep.co.uk, hannah.rossiter@...chnetix.com,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        bsp-development.geo@...ca-geosystems.com
Subject: Re: [PATCH v3 3/3] Input: Add TouchNetix axiom i2c touchscreen driver

Hi Kamel,

just a rough review.

On 23-10-12, Kamel Bouhara wrote:
> Add a new driver for the TouchNetix's axiom family of
> touchscreen controllers. This driver only supports i2c
> and can be later adapted for SPI and USB support.
> 
> Signed-off-by: Kamel Bouhara <kamel.bouhara@...tlin.com>
> ---
>  MAINTAINERS                                   |   1 +
>  drivers/input/touchscreen/Kconfig             |  13 +
>  drivers/input/touchscreen/Makefile            |   1 +
>  .../input/touchscreen/touchnetix_axiom_i2c.c  | 740 ++++++++++++++++++
>  4 files changed, 755 insertions(+)
>  create mode 100644 drivers/input/touchscreen/touchnetix_axiom_i2c.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 12ae8bc6b8cf..2d1e0b025e89 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -21415,6 +21415,7 @@ M:	Kamel Bouhara <kamel.bouhara@...tlin.com>
>  L:	linux-input@...r.kernel.org
>  S:	Maintained
>  F:	Documentation/devicetree/bindings/input/touchscreen/touchnetix,axiom-ax54a.yaml
> +F:	drivers/input/touchscreen/touchnetix_axiom_i2c.c
>  
>  THUNDERBOLT DMA TRAFFIC TEST DRIVER
>  M:	Isaac Hazan <isaac.hazan@...el.com>
> diff --git a/drivers/input/touchscreen/Kconfig b/drivers/input/touchscreen/Kconfig
> index e3e2324547b9..58665ccbe077 100644
> --- a/drivers/input/touchscreen/Kconfig
> +++ b/drivers/input/touchscreen/Kconfig
> @@ -803,6 +803,19 @@ config TOUCHSCREEN_MIGOR
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called migor_ts.
>  
> +config TOUCHSCREEN_TOUCHNETIX_AXIOM_I2C
> +	tristate "TouchNetix AXIOM based touchscreen controllers"
> +	depends on I2C
> +	depends on GPIOLIB || COMPILE_TEST
> +	help
> +	  Say Y here if you have a axiom touchscreen connected to
> +	  your system.
> +
> +	  If unsure, say N.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called axiom_i2c.
> +
>  config TOUCHSCREEN_TOUCHRIGHT
>  	tristate "Touchright serial touchscreen"
>  	select SERIO
> diff --git a/drivers/input/touchscreen/Makefile b/drivers/input/touchscreen/Makefile
> index 62bd24f3ac8e..23b6fb8864b0 100644
> --- a/drivers/input/touchscreen/Makefile
> +++ b/drivers/input/touchscreen/Makefile
> @@ -88,6 +88,7 @@ obj-$(CONFIG_TOUCHSCREEN_SUR40)		+= sur40.o
>  obj-$(CONFIG_TOUCHSCREEN_SURFACE3_SPI)	+= surface3_spi.o
>  obj-$(CONFIG_TOUCHSCREEN_TI_AM335X_TSC)	+= ti_am335x_tsc.o
>  obj-$(CONFIG_TOUCHSCREEN_TOUCHIT213)	+= touchit213.o
> +obj-$(CONFIG_TOUCHSCREEN_TOUCHNETIX_AXIOM_I2C)	+= touchnetix_axiom_i2c.o
>  obj-$(CONFIG_TOUCHSCREEN_TOUCHRIGHT)	+= touchright.o
>  obj-$(CONFIG_TOUCHSCREEN_TOUCHWIN)	+= touchwin.o
>  obj-$(CONFIG_TOUCHSCREEN_TS4800)	+= ts4800-ts.o
> diff --git a/drivers/input/touchscreen/touchnetix_axiom_i2c.c b/drivers/input/touchscreen/touchnetix_axiom_i2c.c
> new file mode 100644
> index 000000000000..fb6239a87341
> --- /dev/null
> +++ b/drivers/input/touchscreen/touchnetix_axiom_i2c.c
> @@ -0,0 +1,740 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * TouchNetix aXiom Touchscreen Driver
> + *
> + * Copyright (C) 2020-2023 TouchNetix Ltd.
> + *
> + * Author(s): Bart Prescott <bartp@...sheep.co.uk>
> + *            Pedro Torruella <pedro.torruella@...chnetix.com>
> + *            Mark Satterthwaite <mark.satterthwaite@...chnetix.com>
> + *            Hannah Rossiter <hannah.rossiter@...chnetix.com>
> + *            Kamel Bouhara <kamel.bouhara@...tlin.com>
> + *
> + */
> +
> +#include <linux/crc16.h>
> +#include <linux/delay.h>
> +#include <linux/device.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/i2c.h>
> +#include <linux/input.h>
> +#include <linux/input/mt.h>
> +#include <linux/interrupt.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/pm.h>
> +#include <linux/slab.h>
> +#include <linux/string.h>

Can you please check if all headers are required e.g. sting.h
seems a bit suspicious here.

> +/*
> + * Runtime TCP mode: device is executing normal code and is
> + * accessible via the Touch Controller Mode
> + */
> +#define BOOT_TCP			0
> +/*
> + * Bootloader BLP mode: device is executing bootloader and is
> + * accessible via the Boot Loader Protocol.
> + */
> +#define BOOT_BLP			1

Both defines are not used.

> +#define AXIOM_PROX_LEVEL		-128
> +/*
> + * Register group u31 has 2 pages for usage table entries.
> + * (2 * AXIOM_COMMS_PAGE_SIZE) / AXIOM_U31_BYTES_PER_USAGE = 85
> + */
> +#define AXIOM_U31_MAX_USAGES		85

The programmer's guid describe the usage as hexadecimal number prefixed
with an 'u'. The current range is from u00 till uFF, so the max. usages
should be 0xff.

> +#define AXIOM_U31_BYTES_PER_USAGE	6
> +#define AXIOM_U31_PAGE0_LENGTH		0x0C
> +#define AXIOM_U31_BOOTMODE_MASK		BIT(7)
> +#define AXIOM_U31_FW_INFO_VARIANT_MASK	GENMASK(6, 0)
> +#define AXIOM_U31_FW_INFO_STATUS_MASK	BIT(7)
> +
> +#define AXIOM_U41_MAX_TARGETS		10
> +
> +#define AXIOM_U46_AUX_CHANNELS		4
> +#define AXIOM_U46_AUX_MASK		GENMASK(11, 0)

I'm still not very happy with the decoding, since the so called
'protocol' is clear and versioned we can add the all required protocols
as struct which has far less magic offsets.

> +
> +#define AXIOM_COMMS_MAX_USAGE_PAGES	3
> +#define AXIOM_COMMS_PAGE_SIZE		256
> +#define AXIOM_COMMS_OVERFLOW_MASK	BIT(7)
> +#define AXIOM_COMMS_REPORT_LEN_MASK	GENMASK(7, 0)
> +
> +#define AXIOM_REBASELINE_CMD		0x03
> +
> +#define AXIOM_REPORT_USAGE_ID		0x34
> +#define AXIOM_DEVINFO_USAGE_ID		0x31
> +#define AXIOM_USAGE_2HB_REPORT_ID	0x01
> +#define AXIOM_REBASELINE_USAGE_ID	0x02
> +#define AXIOM_USAGE_2AUX_REPORT_ID	0x46
> +#define AXIOM_USAGE_2DCTS_REPORT_ID	0x41
> +
> +#define AXIOM_PAGE_MASK			GENMASK(15, 8)

Unused

> +#define AXIOM_PAGE_OFFSET_MASK		GENMASK(7, 0)
> +
> +struct axiom_devinfo {
> +	char bootloader_fw_major;
> +	char bootloader_fw_minor;
> +	char bootmode;
> +	u16 device_id;
> +	char fw_major;
> +	char fw_minor;
> +	char fw_info_extra;
> +	char tcp_revision;
> +	u16 jedec_id;
> +	char num_usages;
> +	char silicon_revision;
> +};
> +
> +/*
> + * Describes parameters of a specific usage, essenstially a single element of
> + * the "Usage Table"
> + */
> +struct usage_entry {
> +	char id;
> +	char is_report;
> +	char start_page;
> +	char num_pages;
> +};
> +
> +/*
> + * Holds state of a touch or target when detected prior a touch (eg.
> + * hover or proximity events).
> + */
> +enum axiom_target_state {
> +	TARGET_STATE_NOT_PRESENT = 0,
> +	TARGET_STATE_PROX = 1,
> +	TARGET_STATE_HOVER = 2,
> +	TARGET_STATE_TOUCHING = 3,
> +	TARGET_STATE_MIN = TARGET_STATE_NOT_PRESENT,
> +	TARGET_STATE_MAX = TARGET_STATE_TOUCHING,

STATE_MIN/MAX not used.

> +};
> +
> +struct u41_target {
> +	enum axiom_target_state state;
> +	u16 x;
> +	u16 y;
> +	s8 z;
> +	bool insert;
> +	bool touch;
> +};
> +
> +struct axiom_target_report {
> +	u8 index;
> +	u8 present;
> +	u16 x;
> +	u16 y;
> +	s8 z;
> +};
> +
> +struct axiom_cmd_header {
> +	u16 target_address;
> +	u16 length:15;
> +	u16 read:1;
> +} __packed;
> +
> +struct axiom_data {
> +	struct axiom_devinfo devinfo;
> +	struct device *dev;
> +	struct gpio_desc *reset_gpio;
> +	struct gpio_desc *irq_gpio;

No need to store the irq_gpio here.

> +	struct i2c_client *client;
> +	struct input_dev *input_dev;
> +	u32 max_report_len;
> +	u32 report_overflow_counter;
> +	u32 report_counter;
> +	char rx_buf[AXIOM_COMMS_MAX_USAGE_PAGES * AXIOM_COMMS_PAGE_SIZE];
> +	struct u41_target targets[AXIOM_U41_MAX_TARGETS];
> +	struct usage_entry usage_table[AXIOM_U31_MAX_USAGES];
> +	bool usage_table_populated;
> +};
> +
> +/*
> + * aXiom devices are typically configured to report
> + * touches at a rate of 100Hz (10ms). For systems
> + * that require polling for reports, 100ms seems like
> + * an acceptable polling rate.
> + * When reports are polled, it will be expected to
> + * occasionally observe the overflow bit being set
> + * in the reports. This indicates that reports are not
> + * being read fast enough.
> + */
> +#define POLL_INTERVAL_DEFAULT_MS 100

Above you describe that the touch-rate is ~10ms why do we configure it
10-times lower here? Also 100ms is huge if you think about user respone
time.

> +/* Translate usage/page/offset triplet into physical address. */
> +static u16
> +usage_to_target_address(struct axiom_data *ts, char usage, char page,
> +			char offset)
> +{
> +	struct axiom_devinfo *device_info;
> +	struct usage_entry *usage_table;
> +	u32 i;
> +
> +	device_info = &ts->devinfo;
> +	usage_table = ts->usage_table;
> +
> +	/* At the moment the convention is that u31 is always at physical address 0x0 */
> +	if (!ts->usage_table_populated) {
> +		if (usage == AXIOM_DEVINFO_USAGE_ID)
> +			return ((page << 8) + offset);
> +		else
> +			return 0xffff;
> +	}
> +
> +	for (i = 0; i < device_info->num_usages; i++) {
> +		if (usage_table[i].id != usage)
> +			continue;
> +
> +		if (page >= usage_table[i].num_pages) {
> +			dev_err(ts->dev, "Invalid usage table! usage: %u, page: %u, offset: %u\n",
> +				usage, page, offset);
> +			return 0xffff;
> +		}
> +	}

We can avoid this loop if we store the usage table exactly as it is,
e.g.:

	usage_table[0x31] = u31;
	usage_table[0x41] = u41;

> +	return ((usage_table[i].start_page + page) << 8) + offset;
> +}
> +
> +static int
> +axiom_i2c_read(struct i2c_client *client, u8 usage, u8 page, u8 *buf, u16 len)
> +{
> +	struct axiom_data *ts = i2c_get_clientdata(client);
> +	struct axiom_cmd_header cmd_header;
> +	struct i2c_msg msg[2];
> +	int ret;
> +
> +	cmd_header.target_address = cpu_to_le16(usage_to_target_address(ts, usage, page, 0));
> +	cmd_header.length = cpu_to_le16(len);
> +	cmd_header.read = 1;
> +
> +	msg[0].addr = client->addr;
> +	msg[0].flags = 0;
> +	msg[0].len = sizeof(cmd_header);
> +	msg[0].buf = (u8 *)&cmd_header;
> +
> +	msg[1].addr = client->addr;
> +	msg[1].flags = I2C_M_RD;
> +	msg[1].len = len;
> +	msg[1].buf = (char *)buf;
> +
> +	ret = i2c_transfer(client->adapter, msg, 2);
> +	if (ret != ARRAY_SIZE(msg)) {
> +		dev_err(&client->dev,
> +			"Failed reading usage %#x page %#x, error=%d\n",
> +			usage, page, ret);
> +		return -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +static int
> +axiom_i2c_write(struct i2c_client *client, u8 usage, u8 page, u8 *buf, u16 len)
> +{
> +	struct axiom_data *ts = i2c_get_clientdata(client);
> +	struct axiom_cmd_header cmd_header;
> +	struct i2c_msg msg[2];
> +	int ret;
> +
> +	cmd_header.target_address = cpu_to_le16(usage_to_target_address(ts, usage, page, 0));
> +	cmd_header.length = cpu_to_le16(len);
> +	cmd_header.read = 0;
> +
> +	msg[0].addr = client->addr;
> +	msg[0].flags = 0;
> +	msg[0].len = sizeof(cmd_header);
> +	msg[0].buf = (u8 *)&cmd_header;
> +
> +	msg[1].addr = client->addr;
> +	msg[1].flags = 0;
> +	msg[1].len = len;
> +	msg[1].buf = (char *)buf;

Please check the "comms protocol app note", for write it is not allowed
to send a stop, so the whole data must be send in one i2c_msg.

> +
> +	ret = i2c_transfer(client->adapter, msg, 2);
> +	if (ret < 0) {
> +		dev_err(&client->dev,
> +			"Failed to write usage %#x page %#x, error=%d\n", usage,
> +			page, ret);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * Decodes and populates the local Usage Table.
> + * Given a buffer of data read from page 1 onwards of u31 from an aXiom
> + * device.
> + */
> +static u32 axiom_populate_usage_table(struct axiom_data *ts, char *rx_data)
> +{
> +	u32 usage_id = 0;
> +	u32 max_report_len = 0;
> +	struct axiom_devinfo *device_info;
> +	struct usage_entry *usage_table;
> +
> +	device_info = &ts->devinfo;
> +	usage_table = ts->usage_table;
> +
> +	for (usage_id = 0; usage_id < device_info->num_usages; usage_id++) {
> +		u16 offset = (usage_id * AXIOM_U31_BYTES_PER_USAGE);
> +		char id = rx_data[offset + 0];
> +		char start_page = rx_data[offset + 1];
> +		char num_pages = rx_data[offset + 2];
> +		u32 max_offset = ((rx_data[offset + 3] & AXIOM_PAGE_OFFSET_MASK) + 1) * 2;
> +
> +		if (!num_pages)
> +			usage_table[usage_id].is_report = true;
> +
> +		/* Store the entry into the usage table */
> +		usage_table[usage_id].id = id;
> +		usage_table[usage_id].start_page = start_page;
> +		usage_table[usage_id].num_pages = num_pages;
> +
> +		dev_dbg(ts->dev, "Usage %2u Info: %*ph\n", usage_id,
> +			AXIOM_U31_BYTES_PER_USAGE,
> +			&rx_data[offset]);
> +
> +		/* Identify the max report length the module will receive */
> +		if (usage_table[usage_id].is_report && max_offset > max_report_len)
> +			max_report_len = max_offset;
> +	}

As said, the sorting can be really easy:

		usage_table[0x01] = u01;
		usage_table[0x31] = u31;

> +	ts->usage_table_populated = true;
> +
> +	return max_report_len;
> +}
> +
> +/* Retrieve, store and print the axiom device information */
> +static int axiom_discover(struct axiom_data *ts)
> +{
> +	struct axiom_devinfo *devinfo = &ts->devinfo;
> +	struct device *dev = ts->dev;
> +	char *rx_data = ts->rx_buf;
> +	int ret;
> +
> +	/*
> +	 * Fetch the first page of usage u31 to get the
> +	 * device information and the number of usages
> +	 */
> +	ret = axiom_i2c_read(ts->client, AXIOM_DEVINFO_USAGE_ID, 0, rx_data,
> +			     AXIOM_U31_PAGE0_LENGTH);
> +	if (ret)
> +		return ret;
> +
> +	devinfo->bootmode = (rx_data[0] & AXIOM_U31_BOOTMODE_MASK);
> +	devinfo->device_id = ((rx_data[1] & AXIOM_PAGE_OFFSET_MASK) << 8) | rx_data[0];
> +	devinfo->fw_minor = rx_data[2];
> +	devinfo->fw_major = rx_data[3];
> +	devinfo->fw_info_extra = rx_data[4];
> +	devinfo->bootloader_fw_minor = rx_data[6];
> +	devinfo->bootloader_fw_major = rx_data[7];
> +	devinfo->jedec_id = (rx_data[8]) | (rx_data[9] << 8);
> +	devinfo->num_usages = rx_data[10];
> +	devinfo->silicon_revision = rx_data[11];
> +
> +	dev_dbg(dev, "  Boot Mode: %s\n", ts->devinfo.bootmode ? "BLP" : "TCP");
> +	dev_dbg(dev, "  Device ID      : %04x\n", ts->devinfo.device_id);
> +	dev_dbg(dev, "  Firmware Rev   : %02x.%02x\n", ts->devinfo.fw_major,
> +		ts->devinfo.fw_minor);
> +	dev_dbg(dev, "  Bootloader Rev : %02x.%02x\n",
> +		ts->devinfo.bootloader_fw_major,
> +		ts->devinfo.bootloader_fw_minor);
> +	dev_dbg(dev, "  FW Extra Info  : %04x\n", ts->devinfo.fw_info_extra);
> +	dev_dbg(dev, "  Silicon        : %02x\n", ts->devinfo.jedec_id);
> +	dev_dbg(dev, "  Num Usages     : %04x\n", ts->devinfo.num_usages);
> +
> +	/* Read the second page of usage u31 to get the usage table */
> +	ret = axiom_i2c_read(ts->client, AXIOM_DEVINFO_USAGE_ID, 1, rx_data,
> +			     (AXIOM_U31_BYTES_PER_USAGE * ts->devinfo.num_usages));
> +	if (ret)
> +		return ret;
> +
> +	ts->max_report_len = axiom_populate_usage_table(ts, rx_data);
> +	dev_dbg(dev, "Max Report Length: %u\n", ts->max_report_len);
> +
> +	return 0;
> +}
> +
> +/*
> + * Support function to axiom_process_u41_report.
> + * Generates input-subsystem events for every target.
> + * After calling this function the caller shall issue
> + * a Sync to the input sub-system.
> + */
> +static bool
> +axiom_process_u41_report_target(struct axiom_data *ts,
> +				struct axiom_target_report *target)
> +{
> +	struct input_dev *input_dev = ts->input_dev;
> +	enum axiom_target_state current_state;
> +	struct u41_target *target_prev_state;
> +	struct device *dev = ts->dev;
> +	bool update = false;
> +	int slot;
> +
> +	/* Verify the target index */
> +	if (target->index >= AXIOM_U41_MAX_TARGETS) {
> +		dev_dbg(dev, "Invalid target index! %u\n", target->index);
> +		return false;
> +	}
> +
> +	target_prev_state = &ts->targets[target->index];
> +
> +	current_state = TARGET_STATE_NOT_PRESENT;
> +
> +	if (target->present) {
> +		if (target->z >= 0)
> +			current_state = TARGET_STATE_TOUCHING;
> +		else if (target->z > AXIOM_PROX_LEVEL && target->z < 0)
> +			current_state = TARGET_STATE_HOVER;
> +		else if (target->z AXIOM_PROX_LEVEL)
> +			current_state = TARGET_STATE_PROX;
> +	}
> +
> +	if (target_prev_state->state == current_state &&
> +	    target_prev_state->x == target->x &&
> +	    target_prev_state->y == target->y &&
> +	    target_prev_state->z == target->z) {
> +		return false;
> +	}
> +
> +	slot = target->index;
> +
> +	dev_dbg(dev, "U41 Target T%u, slot:%u present:%u, x:%u, y:%u, z:%d\n",
> +		target->index, slot, target->present,
> +		target->x, target->y, target->z);
> +
> +	switch (current_state) {
> +	case TARGET_STATE_NOT_PRESENT:
> +	case TARGET_STATE_PROX:
> +		if (target_prev_state->insert)
> +			break;
> +		update = true;
> +		target_prev_state->insert = false;
> +		input_mt_slot(input_dev, slot);
> +
> +		if (!slot)
> +			input_report_key(input_dev, BTN_LEFT, 0);
> +
> +		input_mt_report_slot_inactive(input_dev);
> +		/*
> +		 * make sure the previous coordinates are
> +		 * all off screen when the finger comes back
> +		 */
> +		target->x = 65535;
> +		target->y = 65535;
> +		target->z = AXIOM_PROX_LEVEL;
> +		break;
> +	case TARGET_STATE_HOVER:
> +	case TARGET_STATE_TOUCHING:
> +		target_prev_state->insert = true;
> +		update = true;
> +		input_mt_slot(input_dev, slot);
> +		input_report_abs(input_dev, ABS_MT_TRACKING_ID, slot);
> +		input_report_abs(input_dev, ABS_MT_POSITION_X, target->x);
> +		input_report_abs(input_dev, ABS_X, target->x);
> +		input_report_abs(input_dev, ABS_MT_POSITION_Y, target->y);
> +		input_report_abs(input_dev, ABS_Y, target->y);
> +
> +		if (current_state == TARGET_STATE_TOUCHING) {
> +			input_report_abs(input_dev, ABS_MT_DISTANCE, 0);
> +			input_report_abs(input_dev, ABS_DISTANCE, 0);
> +			input_report_abs(input_dev, ABS_MT_PRESSURE, target->z);
> +			input_report_abs(input_dev, ABS_PRESSURE, target->z);
> +		} else {
> +			input_report_abs(input_dev, ABS_MT_DISTANCE, -target->z);
> +			input_report_abs(input_dev, ABS_DISTANCE, -target->z);
							   	  ^
						      Is this valid?
> +			input_report_abs(input_dev, ABS_MT_PRESSURE, 0);
> +			input_report_abs(input_dev, ABS_PRESSURE, 0);
> +		}
> +
> +		if (!slot)
> +			input_report_key(input_dev, BTN_LEFT, (current_state ==
> +					 TARGET_STATE_TOUCHING));
> +		break;
> +	}
> +
> +	target_prev_state->state = current_state;
> +	target_prev_state->x = target->x;
> +	target_prev_state->y = target->y;
> +	target_prev_state->z = target->z;
> +
> +	if (update)
> +		input_mt_sync_frame(input_dev);
> +
> +	return update;
> +}
> +
> +/*
> + * Take a raw buffer with u41 report data and decode it.
> + * Also generate input events if needed.
> + * rx_buf: ptr to a byte array [0]: Usage number [1]: Status LSB [2]: Status MSB
> + */
> +static void axiom_process_u41_report(struct axiom_data *ts, char *rx_buf)
> +{
> +	struct input_dev *input_dev = ts->input_dev;
> +	struct axiom_target_report target;
> +	bool update_done = false;
> +	u16 target_status;
> +	u32 i;
> +
> +	target_status = ((rx_buf[1]) | (rx_buf[2] << 8));
> +
> +	for (i = 0; i < AXIOM_U41_MAX_TARGETS; i++) {
> +		char target_step = rx_buf[(i * 4)];
> +
> +		target.index = i;
> +		target.present = ((target_status & (1 << i)) != 0) ? 1 : 0;
> +		target.x = ((target_step + 3) | ((target_step + 4) << 8));
> +		target.y = ((target_step + 5) | ((target_step + 6) << 8));
> +		target.z = (s8)(rx_buf[i + 43]);
> +		update_done |= axiom_process_u41_report_target(ts, &target);
> +	}
> +
> +	if (update_done)
> +		input_sync(input_dev);
> +}
> +
> +static void axiom_process_u46_report(struct axiom_data *ts, char *rx_buf)
> +{
> +	struct input_dev *input_dev = ts->input_dev;
> +	u32 event_value;
> +	u16 aux_value;
> +	u32 i = 0;
> +
> +	for (i = 0; i < AXIOM_U46_AUX_CHANNELS; i++) {
> +		char target_step = rx_buf[(i * 2)];
> +
> +		aux_value = (((target_step + 2) << 8) | (target_step + 1)) & AXIOM_U46_AUX_MASK;
> +		event_value = (i << 16) | (aux_value);
> +		input_event(input_dev, EV_MSC, MSC_RAW, event_value);
> +	}
> +
> +	input_mt_sync(input_dev);
> +	input_sync(input_dev);
> +}
> +
> +/*
> + * Validates the crc and demultiplexes the axiom reports to the appropriate
> + * report handler
> + */
> +static void axiom_handle_events(struct axiom_data *ts)
> +{
> +	char *report_data = ts->rx_buf;
> +	struct device *dev = ts->dev;
> +	char usage = report_data[1];
> +	u16 crc_report;
> +	u16 crc_calc;
> +	char len;
> +
> +	axiom_i2c_read(ts->client, AXIOM_REPORT_USAGE_ID, 0, report_data, ts->max_report_len);
> +
> +	if ((report_data[0] & AXIOM_COMMS_OVERFLOW_MASK) != 0)
> +		ts->report_overflow_counter++;
> +
> +	len = (report_data[0] & AXIOM_COMMS_REPORT_LEN_MASK) * 2;
> +	if (!len) {
> +		dev_err(dev, "Zero length report discarded.\n");
> +		return;
> +	}
> +
> +	dev_dbg(dev, "Payload Data %*ph\n", len, report_data);
> +
> +	/* Validate the report CRC */
> +	crc_report = (report_data[len - 1] << 8) | (report_data[len - 2]);
> +	/* Length is in 16 bit words and remove the size of the CRC16 itself */
> +	crc_calc = crc16(0, report_data, (len - 2));
> +
> +	if (crc_calc != crc_report) {
> +		dev_err(dev,
> +			"CRC mismatch! Expected: %#x, Calculated CRC: %#x.\n",
> +			crc_report, crc_calc);
> +		return;
> +	}
> +
> +	switch (usage) {
> +	case AXIOM_USAGE_2DCTS_REPORT_ID:
> +		axiom_process_u41_report(ts, &report_data[1]);
> +		break;
> +
> +	case AXIOM_USAGE_2AUX_REPORT_ID:
> +		/* This is an aux report (force) */
> +		axiom_process_u46_report(ts, &report_data[1]);
> +		break;
> +
> +	case AXIOM_USAGE_2HB_REPORT_ID:
> +		/* This is a heartbeat report */
> +		break;
> +	}
> +
> +	ts->report_counter++;
> +}
> +
> +static void axiom_i2c_poll(struct input_dev *input_dev)
> +{
> +	struct axiom_data *ts = input_get_drvdata(input_dev);
> +
> +	axiom_handle_events(ts);
> +}
> +
> +static irqreturn_t axiom_irq(int irq, void *dev_id)
> +{
> +	struct axiom_data *ts = dev_id;
> +
> +	axiom_handle_events(ts);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void axiom_reset(struct gpio_desc *reset_gpio)
> +{
> +	gpiod_set_value_cansleep(reset_gpio, 1);
> +	usleep_range(1000, 2000);
> +	gpiod_set_value_cansleep(reset_gpio, 0);
> +	msleep(100);
> +}
> +
> +/* Rebaseline the touchscreen, effectively zero-ing it */
> +static int axiom_rebaseline(struct axiom_data *ts)
> +{
> +	char buffer[8] = {};
> +
> +	buffer[0] = AXIOM_REBASELINE_CMD;
> +
> +	return axiom_i2c_write(ts->client, AXIOM_REPORT_USAGE_ID, 0, buffer, sizeof(buffer));
> +}
> +
> +static int axiom_i2c_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct input_dev *input_dev;
> +	struct axiom_data *ts;
> +	int ret;
> +	int target;
> +
> +	ts = devm_kzalloc(dev, sizeof(*ts), GFP_KERNEL);
> +	if (!ts)
> +		return -ENOMEM;
> +
> +	ts->client = client;
> +	i2c_set_clientdata(client, ts);
> +	ts->dev = dev;
> +
> +	ts->irq_gpio = devm_gpiod_get_optional(dev, "irq", GPIOD_IN);
> +	if (IS_ERR(ts->irq_gpio))
> +		return dev_err_probe(dev, PTR_ERR(ts->irq_gpio), "failed to get irq GPIO");

Nope you removed this from the binding.

> +	ts->reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
> +	if (IS_ERR(ts->reset_gpio))
> +		return dev_err_probe(dev, PTR_ERR(ts->reset_gpio), "failed to get reset GPIO\n");

Please also add a regulator for the VDDI/VDDA which is required for the
device to work properly.

> +	axiom_reset(ts->reset_gpio);
> +
> +	if (ts->irq_gpio) {

Nope, please drop the ts->irq_gpio check.

> +		ret = devm_request_threaded_irq(dev, client->irq, NULL,
> +						axiom_irq, 0, dev_name(dev), ts);
> +		if (ret < 0)

If the threaded_irq does fail you can fallback to the polling mode.

> +			return dev_err_probe(dev, ret, "Failed to request threaded IRQ\n");
> +	}
> +
> +	ret = axiom_discover(ts);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed touchscreen discover\n");
> +
> +	ret = axiom_rebaseline(ts);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed touchscreen re-baselining\n");
> +
> +	input_dev = devm_input_allocate_device(ts->dev);
> +	if (!input_dev)
> +		return -ENOMEM;
> +
> +	input_dev->name = "TouchNetix aXiom Touchscreen";
> +	input_dev->phys = "input/axiom_ts";
> +
> +	/* Single Touch */
> +	input_set_abs_params(input_dev, ABS_X, 0, 65535, 0, 0);
> +	input_set_abs_params(input_dev, ABS_Y, 0, 65535, 0, 0);
> +
> +	/* Multi Touch */
> +	/* Min, Max, Fuzz (expected noise in px, try 4?) and Flat */
> +	input_set_abs_params(input_dev, ABS_MT_POSITION_X, 0, 65535, 0, 0);
> +	/* Min, Max, Fuzz (expected noise in px, try 4?) and Flat */
> +	input_set_abs_params(input_dev, ABS_MT_POSITION_Y, 0, 65535, 0, 0);
> +	input_set_abs_params(input_dev, ABS_MT_TOOL_TYPE, 0, MT_TOOL_MAX, 0, 0);
> +	input_set_abs_params(input_dev, ABS_MT_DISTANCE, 0, 127, 0, 0);
> +	input_set_abs_params(input_dev, ABS_MT_PRESSURE, 0, 127, 0, 0);
> +
> +	/* Registers the axiom device as a touchscreen instead of as a mouse pointer */
> +	input_mt_init_slots(input_dev, AXIOM_U41_MAX_TARGETS, INPUT_MT_DIRECT);
> +
> +	input_set_capability(input_dev, EV_KEY, BTN_LEFT);
> +
> +	/* Enables the raw data for up to 4 force channels to be sent to the input subsystem */
> +	set_bit(EV_REL, input_dev->evbit);
> +	set_bit(EV_MSC, input_dev->evbit);
> +	/* Declare that we support "RAW" Miscellaneous events */
> +	set_bit(MSC_RAW, input_dev->mscbit);
> +
> +	if (!ts->irq_gpio) {
> +		ret = input_setup_polling(input_dev, axiom_i2c_poll);
> +		if (ret)
> +			return	dev_err_probe(ts->dev, ret, "Unable to set up polling mode\n");
> +		input_set_poll_interval(input_dev, POLL_INTERVAL_DEFAULT_MS);
> +	}
> +
> +	ts->input_dev = input_dev;
> +	input_set_drvdata(ts->input_dev, ts);
> +
> +	/* Ensure that all reports are initialised to not be present. */
> +	for (target = 0; target < AXIOM_U41_MAX_TARGETS; target++)
> +		ts->targets[target].state = TARGET_STATE_NOT_PRESENT;
> +
> +	ret = input_register_device(input_dev);
> +
> +	if (ret)
> +		return dev_err_probe(ts->dev, ret,
> +					"Could not register with Input Sub-system.\n");
> +
> +	return 0;
> +}
> +
> +static void axiom_i2c_remove(struct i2c_client *client)
> +{
> +	struct axiom_data *ts = i2c_get_clientdata(client);
> +
> +	input_unregister_device(ts->input_dev);

This can be part of devm_add_action_or_reset() and we could remove the
.remove() callback for this driver.

> +}
> +
> +static const struct i2c_device_id axiom_i2c_id_table[] = {
> +	{ "axiom-ax54a" },

Albeit the datasheet says: "axiom ax54a" I think ax stands for axiom. So
the name should be "ax54a" only?

> +	{},

Nit:  { },
> +};
> +

Please drop the unnecessary newline.

> +MODULE_DEVICE_TABLE(i2c, axiom_i2c_id_table);
> +
> +static const struct of_device_id axiom_i2c_of_match[] = {
> +	{ .compatible = "touchnetix,axiom-ax54a", },
> +	{}

same here.

> +};
> +

same here.

> +MODULE_DEVICE_TABLE(of, axiom_i2c_of_match);
> +
> +static struct i2c_driver axiom_i2c_driver = {
> +	.driver = {
> +		   .name = "axiom",
> +		   .of_match_table = axiom_i2c_of_match,
> +	},
> +	.id_table = axiom_i2c_id_table,
> +	.probe = axiom_i2c_probe,
> +	.remove = axiom_i2c_remove,
> +};
> +

same here.

> +module_i2c_driver(axiom_i2c_driver);
> +
> +MODULE_AUTHOR("Bart Prescott <bartp@...sheep.co.uk>");
> +MODULE_AUTHOR("Pedro Torruella <pedro.torruella@...chnetix.com>");
> +MODULE_AUTHOR("Mark Satterthwaite <mark.satterthwaite@...chnetix.com>");
> +MODULE_AUTHOR("Hannah Rossiter <hannah.rossiter@...chnetix.com>");
> +MODULE_AUTHOR("Kamel Bouhara <kamel.bouhara@...tlin.com>");
> +MODULE_DESCRIPTION("TouchNetix aXiom touchscreen I2C bus driver");
> +MODULE_LICENSE("GPL");
> -- 
> 2.25.1
> 
> 

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