gpiolib: pcf857x i2c gpio expander support

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).

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 has been a big factor in the proliferation
of board-specific drivers for these chips...  stuff that rarely makes it
upstream since it's so ugly.  This driver will let such boards use standard
calls.

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 (there's a clear
either/or disjunction).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Jean Delvare <khali@linux-fr.org>
Cc: Eric Miao <eric.miao@marvell.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Philipp Zabel <philipp.zabel@gmail.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Ben Gardner <bgardner@wabtec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 399 insertions, 0 deletions

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 560687c4667e..36d5d6aefc0e 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -27,6 +27,29 @@ config DEBUG_GPIO
 
 comment "I2C GPIO expanders:"
 
+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.
+
 comment "SPI GPIO expanders:"
 
 endmenu
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index c3da03975d58..b469ab24fb11 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -4,3 +4,4 @@ ccflags-$(CONFIG_DEBUG_GPIO)	+= -DDEBUG
 
 obj-$(CONFIG_HAVE_GPIO_LIB)     += gpiolib.o
 
+obj-$(CONFIG_GPIO_PCF857X)      += pcf857x.o
diff --git a/drivers/gpio/pcf857x.c b/drivers/gpio/pcf857x.c
new file mode 100644
index 000000000000..c6b3b5378384
--- /dev/null
+++ b/drivers/gpio/pcf857x.c
@@ -0,0 +1,330 @@
+/*
+ * 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.
+ *
+ * Many other I2C GPIO expander chips (like the pca953x models) have
+ * more complex register models and more conventional circuitry using
+ * push/pull drivers.  They often use the same 0x20..0x27 addresses as
+ * pcf857x parts, making the "legacy" I2C driver model problematic.
+ */
+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 don't 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 don't distinguish here between '75 and '75c 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, but it
+         * may cause transient glitching since it can't know the last value
+         * written (some pins may need to be driven low).
+         *
+         * Using pdata->n_latch avoids that trouble.  When left initialized
+         * to zero, our software copy of the "latch" then matches the chip's
+         * all-ones reset state.  Otherwise it flags pins to be driven low.
+         */
+        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 could use them.
+         */
+        if (pdata->setup) {
+                status = pdata->setup(client,
+                                gpio->chip.base, gpio->chip.ngpio,
+                                pdata->context);
+                if (status < 0)
+                        dev_warn(&client->dev, "setup --> %d\n", 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);
+}
+module_init(pcf857x_init);
+
+static void __exit pcf857x_exit(void)
+{
+        i2c_del_driver(&pcf857x_driver);
+}
+module_exit(pcf857x_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("David Brownell");
diff --git a/include/linux/i2c/pcf857x.h b/include/linux/i2c/pcf857x.h
new file mode 100644
index 000000000000..ba8ea6e16476
--- /dev/null
+++ b/include/linux/i2c/pcf857x.h
@@ -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 */