linux触摸屏驱动分析，touchscreen, struct input_dev,基于TSC2007

代码从2.6.32拷贝：

/*
 * drivers/input/touchscreen/tsc2007.c
 *
 * Copyright (c) 2008 MtekVision Co., Ltd.
 *	Kwangwoo Lee <kwlee@mtekvision.com>
 *
 * Using code from:
 *  - ads7846.c
 *	Copyright (c) 2005 David Brownell
 *	Copyright (c) 2006 Nokia Corporation
 *  - corgi_ts.c
 *	Copyright (C) 2004-2005 Richard Purdie
 *  - omap_ts.[hc], ads7846.h, ts_osk.c
 *	Copyright (C) 2002 MontaVista Software
 *	Copyright (C) 2004 Texas Instruments
 *	Copyright (C) 2005 Dirk Behme
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2 as
 *  published by the Free Software Foundation.
 */
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/input.h>
#include <linux/interrupt.h>
#include <linux/i2c.h>
#include <linux/i2c/tsc2007.h>
#define TS_POLL_DELAY			1 /* ms delay between samples */
#define TS_POLL_PERIOD			1 /* ms delay between samples */
#define TSC2007_MEASURE_TEMP0		(0x0 << 4)
#define TSC2007_MEASURE_AUX		(0x2 << 4)
#define TSC2007_MEASURE_TEMP1		(0x4 << 4)
#define TSC2007_ACTIVATE_XN		(0x8 << 4)
#define TSC2007_ACTIVATE_YN		(0x9 << 4)
#define TSC2007_ACTIVATE_YP_XN		(0xa << 4)
#define TSC2007_SETUP			(0xb << 4)
#define TSC2007_MEASURE_X		(0xc << 4)
#define TSC2007_MEASURE_Y		(0xd << 4)
#define TSC2007_MEASURE_Z1		(0xe << 4)
#define TSC2007_MEASURE_Z2		(0xf << 4)
#define TSC2007_POWER_OFF_IRQ_EN	(0x0 << 2)
#define TSC2007_ADC_ON_IRQ_DIS0		(0x1 << 2)
#define TSC2007_ADC_OFF_IRQ_EN		(0x2 << 2)
#define TSC2007_ADC_ON_IRQ_DIS1		(0x3 << 2)
#define TSC2007_12BIT			(0x0 << 1)
#define TSC2007_8BIT			(0x1 << 1)
#define	MAX_12BIT			((1 << 12) - 1)
#define ADC_ON_12BIT	(TSC2007_12BIT | TSC2007_ADC_ON_IRQ_DIS0)
#define READ_Y		(ADC_ON_12BIT | TSC2007_MEASURE_Y)
#define READ_Z1		(ADC_ON_12BIT | TSC2007_MEASURE_Z1)
#define READ_Z2		(ADC_ON_12BIT | TSC2007_MEASURE_Z2)
#define READ_X		(ADC_ON_12BIT | TSC2007_MEASURE_X)
#define PWRDOWN		(TSC2007_12BIT | TSC2007_POWER_OFF_IRQ_EN)
struct ts_event {
	u16	x;
	u16	y;
	u16	z1, z2;
};
struct tsc2007 {
	struct input_dev	*input;
	char			phys[32];
	struct delayed_work	work;
	struct i2c_client	*client;
	u16			model;
	u16			x_plate_ohms;
	bool			pendown;
	int			irq;
	int			(*get_pendown_state)(void);
	void			(*clear_penirq)(void);
};
static inline int tsc2007_xfer(struct tsc2007 *tsc, u8 cmd)
{
	s32 data;
	u16 val;
	data = i2c_smbus_read_word_data(tsc->client, cmd);
	if (data < 0) {
		dev_err(&tsc->client->dev, "i2c io error: %d/n", data);
		return data;
	}
	/* The protocol and raw data format from i2c interface:
	 * S Addr Wr [A] Comm [A] S Addr Rd [A] [DataLow] A [DataHigh] NA P
	 * Where DataLow has [D11-D4], DataHigh has [D3-D0 << 4 | Dummy 4bit].
	 */
	val = swab16(data) >> 4;
	dev_dbg(&tsc->client->dev, "data: 0x%x, val: 0x%x/n", data, val);
	return val;
}
static void tsc2007_read_values(struct tsc2007 *tsc, struct ts_event *tc)
{
	/* y- still on; turn on only y+ (and ADC) */
	tc->y = tsc2007_xfer(tsc, READ_Y);
	/* turn y- off, x+ on, then leave in lowpower */
	tc->x = tsc2007_xfer(tsc, READ_X);
	/* turn y+ off, x- on; we'll use formula #1 */
	tc->z1 = tsc2007_xfer(tsc, READ_Z1);
	tc->z2 = tsc2007_xfer(tsc, READ_Z2);
	/* Prepare for next touch reading - power down ADC, enable PENIRQ */
	tsc2007_xfer(tsc, PWRDOWN);
}
static u32 tsc2007_calculate_pressure(struct tsc2007 *tsc, struct ts_event *tc)
{
	u32 rt = 0;
	/* range filtering */
	if (tc->x == MAX_12BIT)
		tc->x = 0;
	if (likely(tc->x && tc->z1)) {
		/* compute touch pressure resistance using equation #1 */
		rt = tc->z2 - tc->z1;
		rt *= tc->x;
		rt *= tsc->x_plate_ohms;
		rt /= tc->z1;
		rt = (rt + 2047) >> 12;
	}
	return rt;
}
static void tsc2007_send_up_event(struct tsc2007 *tsc)
{
	struct input_dev *input = tsc->input;
	dev_dbg(&tsc->client->dev, "UP/n");
	input_report_key(input, BTN_TOUCH, 0);
	input_report_abs(input, ABS_PRESSURE, 0);
	input_sync(input);
}
//中断后跑到这里来
static void tsc2007_work(struct work_struct *work)
{
	struct tsc2007 *ts =
		container_of(to_delayed_work(work), struct tsc2007, work);
	struct ts_event tc;
	u32 rt;
	/*
	 * NOTE: We can't rely on the pressure to determine the pen down
	 * state, even though this controller has a pressure sensor.
	 * The pressure value can fluctuate for quite a while after
	 * lifting the pen and in some cases may not even settle at the
	 * expected value.
	 *
	 * The only safe way to check for the pen up condition is in the
	 * work function by reading the pen signal state (it's a GPIO
	 * and IRQ). Unfortunately such callback is not always available,
	 * in that case we have rely on the pressure anyway.
	 */
	if (ts->get_pendown_state) {
		if (unlikely(!ts->get_pendown_state())) {
			tsc2007_send_up_event(ts);
			ts->pendown = false;
			goto out;
		}
		dev_dbg(&ts->client->dev, "pen is still down/n");
	}
	tsc2007_read_values(ts, &tc);
	rt = tsc2007_calculate_pressure(ts, &tc); //计算压力
	if (rt > MAX_12BIT) {
		/*
		 * Sample found inconsistent by debouncing or pressure is
		 * beyond the maximum. Don't report it to user space,
		 * repeat at least once more the measurement.
		 */
		dev_dbg(&ts->client->dev, "ignored pressure %d/n", rt);
		goto out;
	}
	if (rt) {
		struct input_dev *input = ts->input;
		if (!ts->pendown) {
			dev_dbg(&ts->client->dev, "DOWN/n");
			input_report_key(input, BTN_TOUCH, 1);
			ts->pendown = true;
		}
		input_report_abs(input, ABS_X, tc.x);
		input_report_abs(input, ABS_Y, tc.y);
		input_report_abs(input, ABS_PRESSURE, rt);
		input_sync(input);
		dev_dbg(&ts->client->dev, "point(%4d,%4d), pressure (%4u)/n",
			tc.x, tc.y, rt);
	} else if (!ts->get_pendown_state && ts->pendown) {
		/*
		 * We don't have callback to check pendown state, so we
		 * have to assume that since pressure reported is 0 the
		 * pen was lifted up.
		 */
		tsc2007_send_up_event(ts);
		ts->pendown = false;
	}
 out:
	if (ts->pendown)
		schedule_delayed_work(&ts->work,
				      msecs_to_jiffies(TS_POLL_PERIOD));
	else
		enable_irq(ts->irq);
}
static irqreturn_t tsc2007_irq(int irq, void *handle)
{
	struct tsc2007 *ts = handle;
	if (!ts->get_pendown_state || likely(ts->get_pendown_state())) {
		disable_irq_nosync(ts->irq);
		schedule_delayed_work(&ts->work,
				      msecs_to_jiffies(TS_POLL_DELAY));
	}
	if (ts->clear_penirq)
		ts->clear_penirq();
	return IRQ_HANDLED;
}
static void tsc2007_free_irq(struct tsc2007 *ts)
{
	free_irq(ts->irq, ts);
	if (cancel_delayed_work_sync(&ts->work)) {
		/*
		 * Work was pending, therefore we need to enable
		 * IRQ here to balance the disable_irq() done in the
		 * interrupt handler.
		 */
		enable_irq(ts->irq);
	}
}
static int __devinit tsc2007_probe(struct i2c_client *client,
				   const struct i2c_device_id *id)
{
	struct tsc2007 *ts;
	struct tsc2007_platform_data *pdata = pdata = client->dev.platform_data;
	struct input_dev *input_dev;
	int err;
	if (!pdata) {
		dev_err(&client->dev, "platform data is required!/n");
		return -EINVAL;
	}
	if (!i2c_check_functionality(client->adapter,
				     I2C_FUNC_SMBUS_READ_WORD_DATA))
		return -EIO;
	ts = kzalloc(sizeof(struct tsc2007), GFP_KERNEL);
	input_dev = input_allocate_device();
	if (!ts || !input_dev) {
		err = -ENOMEM;
		goto err_free_mem;
	}
	ts->client = client;
	ts->irq = client->irq;
	ts->input = input_dev;
	INIT_DELAYED_WORK(&ts->work, tsc2007_work);
	ts->model             = pdata->model;
	ts->x_plate_ohms      = pdata->x_plate_ohms;
	ts->get_pendown_state = pdata->get_pendown_state;
	ts->clear_penirq      = pdata->clear_penirq;
	snprintf(ts->phys, sizeof(ts->phys),
		 "%s/input0", dev_name(&client->dev));
	input_dev->name = "TSC2007 Touchscreen";
	input_dev->phys = ts->phys;
	input_dev->id.bustype = BUS_I2C;
	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
	input_dev->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
	input_set_abs_params(input_dev, ABS_X, 0, MAX_12BIT, 0, 0);
	input_set_abs_params(input_dev, ABS_Y, 0, MAX_12BIT, 0, 0);
	input_set_abs_params(input_dev, ABS_PRESSURE, 0, MAX_12BIT, 0, 0);
	if (pdata->init_platform_hw)
		pdata->init_platform_hw();
	err = request_irq(ts->irq, tsc2007_irq, 0,
			client->dev.driver->name, ts);
	if (err < 0) {
		dev_err(&client->dev, "irq %d busy?/n", ts->irq);
		goto err_free_mem;
	}
	/* Prepare for touch readings - power down ADC and enable PENIRQ */
	err = tsc2007_xfer(ts, PWRDOWN);
	if (err < 0)
		goto err_free_irq;
	err = input_register_device(input_dev);
	if (err)
		goto err_free_irq;
	i2c_set_clientdata(client, ts);
	return 0;
 err_free_irq:
	tsc2007_free_irq(ts);
	if (pdata->exit_platform_hw)
		pdata->exit_platform_hw();
 err_free_mem:
	input_free_device(input_dev);
	kfree(ts);
	return err;
}
static int __devexit tsc2007_remove(struct i2c_client *client)
{
	struct tsc2007	*ts = i2c_get_clientdata(client);
	struct tsc2007_platform_data *pdata = client->dev.platform_data;
	tsc2007_free_irq(ts);
	if (pdata->exit_platform_hw)
		pdata->exit_platform_hw();
	input_unregister_device(ts->input);
	kfree(ts);
	return 0;
}
static struct i2c_device_id tsc2007_idtable[] = {
	{ "tsc2007", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, tsc2007_idtable);
static struct i2c_driver tsc2007_driver = {
	.driver = {
		.owner	= THIS_MODULE,
		.name	= "tsc2007"
	},
	.id_table	= tsc2007_idtable,
	.probe		= tsc2007_probe,
	.remove		= __devexit_p(tsc2007_remove),
};
static int __init tsc2007_init(void)
{
	return i2c_add_driver(&tsc2007_driver);
}
static void __exit tsc2007_exit(void)
{
	i2c_del_driver(&tsc2007_driver);
}
module_init(tsc2007_init);
module_exit(tsc2007_exit);
MODULE_AUTHOR("Kwangwoo Lee <kwlee@mtekvision.com>");
MODULE_DESCRIPTION("TSC2007 TouchScreen Driver");
MODULE_LICENSE("GPL");

看一遍后就大概知道流程了。

当按下触摸板后产生中断，中断里面调用延时函数进入底半部程序。

在调度函数里面，先读取坐标，计算压力，然后根据压力大小上报坐标。

若触摸板一直按下，那么就重新调用，并通过压力值来看触摸板是否释放。



简单吧？