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    SubjectRe: [patch/rfc 2/4] pcf857x I2C GPIO expander driver
    Date
    On Friday 30 November 2007, David Brownell wrote:
    > Thanks for the review.  I'll snip out typos and similar trivial
    > comments (and fix them!), using responses here for more the
    > substantive feedback.

    Here's the current version of this patch ... updated to put the
    driver into drivers/gpio (separate patch setting that up) and
    the header into <linux/i2c/pcf857x.h>

    Note that after looking at the GPIO expanders listed at the NXP
    website, I updated this to accept a few more of these chips.
    Other than reset pins and addressing options, the key difference
    between these seems to be the top I2C clock speed supported:

    pcf857x ... 100 KHz
    pca857x ... 400 KHz
    pca967x ... 1000 KHz

    Otherwise they're equivalent at the level of just swapping parts.

    - Dave

    ============= SNIP!
    This is a new-style I2C driver for most common 8 and 16 bit I2C based
    "quasi-bidirectional" GPIO expanders: pcf8574 or pcf8575, and several
    compatible models (mostly faster, supporting I2C at up to 1 MHz).

    Since it's a new-style driver, these devices must be configured as
    part of board-specific init. That eliminates the need for error-prone
    manual configuration of module parameters, and makes compatibility
    with legacy drivers (pcf8574.c, pc8575.c)for these chips easier.

    The driver exposes the GPIO signals using the platform-neutral GPIO
    programming interface, so they are easily accessed by other kernel
    code. The lack of such a flexible kernel API is what has ensured
    the proliferation of board-specific drivers for these chips... stuff
    that rarely makes it upstream since it's so ugly. This driver will
    let them use standard calls.

    Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
    ---
    drivers/gpio/Kconfig | 23 +++
    drivers/gpio/Makefile | 2
    drivers/gpio/pcf857x.c | 331 ++++++++++++++++++++++++++++++++++++++++++++
    include/linux/i2c/pcf857x.h | 45 +++++
    4 files changed, 401 insertions(+)

    --- a/drivers/gpio/Kconfig 2007-12-05 15:13:27.000000000 -0800
    +++ b/drivers/gpio/Kconfig 2007-12-05 15:14:12.000000000 -0800
    @@ -5,4 +5,27 @@
    menu "GPIO Support"
    depends on GPIO_LIB

    +config GPIO_PCF857X
    + tristate "PCF857x, PCA857x, and PCA967x I2C GPIO expanders"
    + depends on I2C
    + help
    + Say yes here to provide access to most "quasi-bidirectional" I2C
    + GPIO expanders used for additional digital outputs or inputs.
    + Most of these parts are from NXP, though TI is a second source for
    + some of them. Compatible models include:
    +
    + 8 bits: pcf8574, pcf8574a, pca8574, pca8574a,
    + pca9670, pca9672, pca9674, pca9674a
    +
    + 16 bits: pcf8575, pcf8575c, pca8575,
    + pca9671, pca9673, pca9675
    +
    + Your board setup code will need to declare the expanders in
    + use, and assign numbers to the GPIOs they expose. Those GPIOs
    + can then be used from drivers and other kernel code, just like
    + other GPIOs, but only accessible from task contexts.
    +
    + This driver provides an in-kernel interface to those GPIOs using
    + platform-neutral GPIO calls.
    +
    endmenu
    --- a/drivers/gpio/Makefile 2007-12-05 15:14:03.000000000 -0800
    +++ b/drivers/gpio/Makefile 2007-12-05 15:14:12.000000000 -0800
    @@ -1 +1,3 @@
    # gpio support: dedicated expander chips, etc
    +
    +obj-$(CONFIG_GPIO_PCF857X) += pcf857x.o
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ b/drivers/gpio/pcf857x.c 2007-12-05 15:15:18.000000000 -0800
    @@ -0,0 +1,331 @@
    +/*
    + * pcf857x - driver for pcf857x, pca857x, and pca967x I2C GPIO expanders
    + *
    + * Copyright (C) 2007 David Brownell
    + *
    + * This program is free software; you can redistribute it and/or modify
    + * it under the terms of the GNU General Public License as published by
    + * the Free Software Foundation; either version 2 of the License, or
    + * (at your option) any later version.
    + *
    + * This program is distributed in the hope that it will be useful,
    + * but WITHOUT ANY WARRANTY; without even the implied warranty of
    + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    + * GNU General Public License for more details.
    + *
    + * You should have received a copy of the GNU General Public License
    + * along with this program; if not, write to the Free Software
    + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
    + */
    +
    +#include <linux/kernel.h>
    +#include <linux/slab.h>
    +#include <linux/i2c.h>
    +#include <linux/i2c/pcf857x.h>
    +
    +#include <asm/gpio.h>
    +
    +
    +/*
    + * The pcf857x, pca857x, and pca967x chips only expose one read and one
    + * write register. Writing a "one" bit (to match the reset state) lets
    + * that pin be used as an input; it's not an open-drain model, but acts
    + * a bit like one. This is described as "quasi-bidirectional"; read the
    + * chip documentation for details.
    + *
    + * Some other I2C GPIO expander chips (like the pca953{4,5,6,7,9}, pca9555,
    + * pca9698, mcp23008, and mc23017) have more complex register models with
    + * more conventional input circuitry, often using 0x20..0x27 addresses.
    + */
    +struct pcf857x {
    + struct gpio_chip chip;
    + struct i2c_client *client;
    + unsigned out; /* software latch */
    +};
    +
    +/*-------------------------------------------------------------------------*/
    +
    +/* Talk to 8-bit I/O expander */
    +
    +static int pcf857x_input8(struct gpio_chip *chip, unsigned offset)
    +{
    + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
    +
    + gpio->out |= (1 << offset);
    + return i2c_smbus_write_byte(gpio->client, gpio->out);
    +}
    +
    +static int pcf857x_get8(struct gpio_chip *chip, unsigned offset)
    +{
    + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
    + s32 value;
    +
    + value = i2c_smbus_read_byte(gpio->client);
    + return (value < 0) ? 0 : (value & (1 << offset));
    +}
    +
    +static int pcf857x_output8(struct gpio_chip *chip, unsigned offset, int value)
    +{
    + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
    + unsigned bit = 1 << offset;
    +
    + if (value)
    + gpio->out |= bit;
    + else
    + gpio->out &= ~bit;
    + return i2c_smbus_write_byte(gpio->client, gpio->out);
    +}
    +
    +static void pcf857x_set8(struct gpio_chip *chip, unsigned offset, int value)
    +{
    + pcf857x_output8(chip, offset, value);
    +}
    +
    +/*-------------------------------------------------------------------------*/
    +
    +/* Talk to 16-bit I/O expander */
    +
    +static int i2c_write_le16(struct i2c_client *client, u16 word)
    +{
    + u8 buf[2] = { word & 0xff, word >> 8, };
    + int status;
    +
    + status = i2c_master_send(client, buf, 2);
    + return (status < 0) ? status : 0;
    +}
    +
    +static int i2c_read_le16(struct i2c_client *client)
    +{
    + u8 buf[2];
    + int status;
    +
    + status = i2c_master_recv(client, buf, 2);
    + if (status < 0)
    + return status;
    + return (buf[1] << 8) | buf[0];
    +}
    +
    +static int pcf857x_input16(struct gpio_chip *chip, unsigned offset)
    +{
    + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
    +
    + gpio->out |= (1 << offset);
    + return i2c_write_le16(gpio->client, gpio->out);
    +}
    +
    +static int pcf857x_get16(struct gpio_chip *chip, unsigned offset)
    +{
    + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
    + int value;
    +
    + value = i2c_read_le16(gpio->client);
    + return (value < 0) ? 0 : (value & (1 << offset));
    +}
    +
    +static int pcf857x_output16(struct gpio_chip *chip, unsigned offset, int value)
    +{
    + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
    + unsigned bit = 1 << offset;
    +
    + if (value)
    + gpio->out |= bit;
    + else
    + gpio->out &= ~bit;
    + return i2c_write_le16(gpio->client, gpio->out);
    +}
    +
    +static void pcf857x_set16(struct gpio_chip *chip, unsigned offset, int value)
    +{
    + pcf857x_output16(chip, offset, value);
    +}
    +
    +/*-------------------------------------------------------------------------*/
    +
    +static int pcf857x_probe(struct i2c_client *client)
    +{
    + struct pcf857x_platform_data *pdata;
    + struct pcf857x *gpio;
    + int status;
    +
    + pdata = client->dev.platform_data;
    + if (!pdata)
    + return -ENODEV;
    +
    + /* Allocate, initialize, and register this gpio_chip. */
    + gpio = kzalloc(sizeof *gpio, GFP_KERNEL);
    + if (!gpio)
    + return -ENOMEM;
    +
    + gpio->chip.base = pdata->gpio_base;
    + gpio->chip.can_sleep = 1;
    +
    + /* NOTE: the OnSemi jlc1562b is also largely compatible with
    + * these parts, notably for output. It has a low-resolution
    + * DAC instead of pin change IRQs; and its inputs can be the
    + * result of comparators.
    + */
    +
    + /* 8574 addresses are 0x20..0x27; 8574a uses 0x38..0x3f;
    + * 9670, 9672, 9764, and 9764a use quite a variety.
    + *
    + * NOTE: we dont distinguish here between *4 and *4a parts.
    + */
    + if (strcmp(client->name, "pcf8574") == 0
    + || strcmp(client->name, "pca8574") == 0
    + || strcmp(client->name, "pca9670") == 0
    + || strcmp(client->name, "pca9672") == 0
    + || strcmp(client->name, "pca9674") == 0
    + ) {
    + gpio->chip.ngpio = 8;
    + gpio->chip.direction_input = pcf857x_input8;
    + gpio->chip.get = pcf857x_get8;
    + gpio->chip.direction_output = pcf857x_output8;
    + gpio->chip.set = pcf857x_set8;
    +
    + if (!i2c_check_functionality(client->adapter,
    + I2C_FUNC_SMBUS_BYTE))
    + status = -EIO;
    +
    + /* fail if there's no chip present */
    + else
    + status = i2c_smbus_read_byte(client);
    +
    + /* '75/'75c addresses are 0x20..0x27, just like the '74;
    + * the '75c doesn't have a current source pulling high.
    + * 9671, 9673, and 9765 use quite a variety of addresses.
    + *
    + * NOTE: we dont distinguish here between 8575/8575a parts.
    + */
    + } else if (strcmp(client->name, "pcf8575") == 0
    + || strcmp(client->name, "pca8575") == 0
    + || strcmp(client->name, "pca9671") == 0
    + || strcmp(client->name, "pca9673") == 0
    + || strcmp(client->name, "pca9675") == 0
    + ) {
    + gpio->chip.ngpio = 16;
    + gpio->chip.direction_input = pcf857x_input16;
    + gpio->chip.get = pcf857x_get16;
    + gpio->chip.direction_output = pcf857x_output16;
    + gpio->chip.set = pcf857x_set16;
    +
    + if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
    + status = -EIO;
    +
    + /* fail if there's no chip present */
    + else
    + status = i2c_read_le16(client);
    +
    + } else
    + status = -ENODEV;
    +
    + if (status < 0)
    + goto fail;
    +
    + gpio->chip.label = client->name;
    +
    + gpio->client = client;
    + i2c_set_clientdata(client, gpio);
    +
    + /* NOTE: these chips have strange "quasi-bidirectional" I/O pins.
    + * We can't actually know whether a pin is configured (a) as output
    + * and driving the signal low, or (b) as input and reporting a low
    + * value ... without knowing the last value written since the chip
    + * came out of reset (if any). We can't read the latched output.
    + *
    + * In short, the only reliable solution for setting up pin direction
    + * is to do it explicitly. The setup() method can do that.
    + *
    + * We use pdata->n_latch to avoid trouble. In the typical case it's
    + * left initialized to zero; our software copy of the "latch" then
    + * matches the chip's all-ones reset state. But some systems will
    + * need to drive some pins low, while avoiding transient glitches.
    + * Handle those cases by assigning n_latch to a nonzero value.
    + */
    + gpio->out = ~pdata->n_latch;
    +
    + status = gpiochip_add(&gpio->chip);
    + if (status < 0)
    + goto fail;
    +
    + /* NOTE: these chips can issue "some pin-changed" IRQs, which we
    + * don't yet even try to use. Among other issues, the relevant
    + * genirq state isn't available to modular drivers; and most irq
    + * methods can't be called from sleeping contexts.
    + */
    +
    + dev_info(&client->dev, "gpios %d..%d on a %s%s\n",
    + gpio->chip.base,
    + gpio->chip.base + gpio->chip.ngpio - 1,
    + client->name,
    + client->irq ? " (irq ignored)" : "");
    +
    + /* Let platform code set up the GPIOs and their users.
    + * Now is the first time anyone can use them.
    + */
    + if (pdata->setup) {
    + status = pdata->setup(client,
    + gpio->chip.base, gpio->chip.ngpio,
    + pdata->context);
    + if (status < 0)
    + dev_err(&client->dev, "%s --> %d\n",
    + "setup", status);
    + }
    +
    + return 0;
    +
    +fail:
    + dev_dbg(&client->dev, "probe error %d for '%s'\n",
    + status, client->name);
    + kfree(gpio);
    + return status;
    +}
    +
    +static int pcf857x_remove(struct i2c_client *client)
    +{
    + struct pcf857x_platform_data *pdata = client->dev.platform_data;
    + struct pcf857x *gpio = i2c_get_clientdata(client);
    + int status = 0;
    +
    + if (pdata->teardown) {
    + status = pdata->teardown(client,
    + gpio->chip.base, gpio->chip.ngpio,
    + pdata->context);
    + if (status < 0) {
    + dev_err(&client->dev, "%s --> %d\n",
    + "teardown", status);
    + return status;
    + }
    + }
    +
    + status = gpiochip_remove(&gpio->chip);
    + if (status == 0)
    + kfree(gpio);
    + else
    + dev_err(&client->dev, "%s --> %d\n", "remove", status);
    + return status;
    +}
    +
    +static struct i2c_driver pcf857x_driver = {
    + .driver = {
    + .name = "pcf857x",
    + .owner = THIS_MODULE,
    + },
    + .probe = pcf857x_probe,
    + .remove = pcf857x_remove,
    +};
    +
    +static int __init pcf857x_init(void)
    +{
    + return i2c_add_driver(&pcf857x_driver);
    +}
    +/* we want GPIOs to be ready at device_initcall() time */
    +subsys_initcall(pcf857x_init);
    +
    +static void __exit pcf857x_exit(void)
    +{
    + i2c_del_driver(&pcf857x_driver);
    +}
    +module_exit(pcf857x_exit);
    +
    +MODULE_LICENSE("GPL");
    +MODULE_AUTHOR("David Brownell");
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ b/include/linux/i2c/pcf857x.h 2007-12-05 15:14:12.000000000 -0800
    @@ -0,0 +1,45 @@
    +#ifndef __LINUX_PCF857X_H
    +#define __LINUX_PCF857X_H
    +
    +/**
    + * struct pcf857x_platform_data - data to set up pcf857x driver
    + * @gpio_base: number of the chip's first GPIO
    + * @n_latch: optional bit-inverse of initial register value; if
    + * you leave this initialized to zero the driver will act
    + * like the chip was just reset
    + * @setup: optional callback issued once the GPIOs are valid
    + * @teardown: optional callback issued before the GPIOs are invalidated
    + * @context: optional parameter passed to setup() and teardown()
    + *
    + * In addition to the I2C_BOARD_INFO() state appropriate to each chip,
    + * the i2c_board_info used with the pcf875x driver must provide the
    + * chip "type" ("pcf8574", "pcf8574a", "pcf8575", "pcf8575c") and its
    + * platform_data (pointer to one of these structures) with at least
    + * the gpio_base value initialized.
    + *
    + * The @setup callback may be used with the kind of board-specific glue
    + * which hands the (now-valid) GPIOs to other drivers, or which puts
    + * devices in their initial states using these GPIOs.
    + *
    + * These GPIO chips are only "quasi-bidirectional"; read the chip specs
    + * to understand the behavior. They don't have separate registers to
    + * record which pins are used for input or output, record which output
    + * values are driven, or provide access to input values. That must be
    + * inferred by reading the chip's value and knowing the last value written
    + * to it. If you leave n_latch initialized to zero, that last written
    + * value is presumed to be all ones (as if the chip were just reset).
    + */
    +struct pcf857x_platform_data {
    + unsigned gpio_base;
    + unsigned n_latch;
    +
    + int (*setup)(struct i2c_client *client,
    + int gpio, unsigned ngpio,
    + void *context);
    + int (*teardown)(struct i2c_client *client,
    + int gpio, unsigned ngpio,
    + void *context);
    + void *context;
    +};
    +
    +#endif /* __LINUX_PCF857X_H */
    --
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