diff mbox

[v2,2/4] mfd: add Gateworks System Controller core driver

Message ID 1520287361-12569-3-git-send-email-tharvey@gateworks.com (mailing list archive)
State Changes Requested
Headers show

Commit Message

Tim Harvey March 5, 2018, 10:02 p.m. UTC 
The Gateworks System Controller (GSC) is an I2C slave controller
implemented with an MSP430 micro-controller whose firmware embeds the
following features:
 - I/O expander (16 GPIO's) using PCA955x protocol
 - Real Time Clock using DS1672 protocol
 - User EEPROM using AT24 protocol
 - HWMON using custom protocol
 - Interrupt controller with tamper detect, user pushbotton
 - Watchdog controller capable of full board power-cycle
 - Power Control capable of full board power-cycle

see http://trac.gateworks.com/wiki/gsc for more details

Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Tim Harvey <tharvey@gateworks.com>
---
v2:
- change license comment block style
- remove COMPILE_TEST (Randy)
- fixed whitespace issues
- replaced a printk with dev_err

 drivers/mfd/Kconfig     |  13 ++
 drivers/mfd/Makefile    |   1 +
 drivers/mfd/gsc.c       | 330 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/mfd/gsc.h |  82 ++++++++++++
 4 files changed, 426 insertions(+)
 create mode 100644 drivers/mfd/gsc.c
 create mode 100644 include/linux/mfd/gsc.h

Comments

Lee Jones March 12, 2018, 2:41 p.m. UTC | #1 
On Mon, 05 Mar 2018, Tim Harvey wrote:

> The Gateworks System Controller (GSC) is an I2C slave controller
> implemented with an MSP430 micro-controller whose firmware embeds the
> following features:
>  - I/O expander (16 GPIO's) using PCA955x protocol
>  - Real Time Clock using DS1672 protocol
>  - User EEPROM using AT24 protocol
>  - HWMON using custom protocol
>  - Interrupt controller with tamper detect, user pushbotton
>  - Watchdog controller capable of full board power-cycle
>  - Power Control capable of full board power-cycle
> 
> see http://trac.gateworks.com/wiki/gsc for more details
> 
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Tim Harvey <tharvey@gateworks.com>
> ---
> v2:
> - change license comment block style
> - remove COMPILE_TEST (Randy)
> - fixed whitespace issues
> - replaced a printk with dev_err
> 
>  drivers/mfd/Kconfig     |  13 ++
>  drivers/mfd/Makefile    |   1 +
>  drivers/mfd/gsc.c       | 330 ++++++++++++++++++++++++++++++++++++++++++++++++

I'd prefer gateworks-sc.c

>  include/linux/mfd/gsc.h |  82 ++++++++++++
>  4 files changed, 426 insertions(+)
>  create mode 100644 drivers/mfd/gsc.c
>  create mode 100644 include/linux/mfd/gsc.h
> 
> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
> index 1d20a80..5694013 100644
> --- a/drivers/mfd/Kconfig
> +++ b/drivers/mfd/Kconfig
> @@ -341,6 +341,19 @@ config MFD_EXYNOS_LPASS
>  	  Select this option to enable support for Samsung Exynos Low Power
>  	  Audio Subsystem.
>  
> +config MFD_GSC

Prefer MFD_GATEWORKS_SC

> +	tristate "Gateworks System Controller"
> +	depends on (I2C && OF)
> +	select MFD_CORE
> +	select REGMAP_I2C
> +	select REGMAP_IRQ
> +	help
> +	  Enable support for the Gateworks System Controller found
> +	  on Gateworks Single Board Computers.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called gsc.
> +
>  config MFD_MC13XXX
>  	tristate
>  	depends on (SPI_MASTER || I2C)
> diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> index d9474ad..aede0bc 100644
> --- a/drivers/mfd/Makefile
> +++ b/drivers/mfd/Makefile
> @@ -18,6 +18,7 @@ obj-$(CONFIG_MFD_CROS_EC)	+= cros_ec_core.o
>  obj-$(CONFIG_MFD_CROS_EC_I2C)	+= cros_ec_i2c.o
>  obj-$(CONFIG_MFD_CROS_EC_SPI)	+= cros_ec_spi.o
>  obj-$(CONFIG_MFD_EXYNOS_LPASS)	+= exynos-lpass.o
> +obj-$(CONFIG_MFD_GSC)		+= gsc.o
>  
>  rtsx_pci-objs			:= rtsx_pcr.o rts5209.o rts5229.o rtl8411.o rts5227.o rts5249.o
>  obj-$(CONFIG_MFD_RTSX_PCI)	+= rtsx_pci.o
> diff --git a/drivers/mfd/gsc.c b/drivers/mfd/gsc.c
> new file mode 100644
> index 0000000..4ac400a
> --- /dev/null
> +++ b/drivers/mfd/gsc.c
> @@ -0,0 +1,330 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + *
> + * Copyright (C) 2018 Gateworks Corporation
> + *
> + * The Gateworks System Controller (GSC) is a family of a multi-function
> + * "Power Management and System Companion Device" chips originally designed for
> + * use in Gateworks Single Board Computers. The control interface is I2C,
> + * at 100kbps, with an interrupt.
> + *
> + */
> +#include <linux/device.h>
> +#include <linux/i2c.h>
> +#include <linux/interrupt.h>
> +#include <linux/mfd/core.h>

What's this for?

> +#include <linux/mfd/gsc.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +
> +/*
> + * The GSC suffers from an errata where occasionally during
> + * ADC cycles the chip can NAK i2c transactions. To ensure we have reliable

s/i2c/I2C/

> + * register access we place retries around register access.
> + */
> +#define I2C_RETRIES	3
> +
> +static int gsc_regmap_regwrite(void *context, unsigned int reg,
> +			       unsigned int val)
> +{
> +	struct i2c_client *client = context;
> +	int retry, ret;
> +
> +	for (retry = 0; retry < I2C_RETRIES; retry++) {
> +		ret = i2c_smbus_write_byte_data(client, reg, val);
> +		/*
> +		 * -EAGAIN returned when the i2c host controller is busy
> +		 * -EIO returned when i2c device is busy
> +		 */
> +		if (ret != -EAGAIN && ret != -EIO)
> +			break;
> +	}
> +	if (ret < 0) {
> +		dev_err(&client->dev, ">> 0x%02x %d\n", reg, ret);

">>" doesn't tell the user much.  To the unaware you are spitting out
random characters/values.  Please provide more information in your
error messages.


> +		return ret;
> +	}
> +	dev_dbg(&client->dev, ">> 0x%02x=0x%02x (%d)\n", reg, val, retry);

As above.  Or better still, consider removing this line completely.

> +	return 0;
> +}
> +
> +static int gsc_regmap_regread(void *context, unsigned int reg,
> +			      unsigned int *val)
> +{
> +	struct i2c_client *client = context;
> +	int retry, ret;
> +
> +	for (retry = 0; retry < I2C_RETRIES; retry++) {
> +		ret = i2c_smbus_read_byte_data(client, reg);
> +		/*
> +		 * -EAGAIN returned when the i2c host controller is busy
> +		 * -EIO returned when i2c device is busy
> +		 */
> +		if (ret != -EAGAIN && ret != -EIO)
> +			break;
> +	}
> +	if (ret < 0) {
> +		dev_err(&client->dev, "<< 0x%02x %d\n", reg, ret);

As above.

> +		return ret;
> +	}
> +
> +	*val = ret & 0xff;
> +	dev_dbg(&client->dev, "<< 0x%02x=0x%02x (%d)\n", reg, *val, retry);

As above.

> +	return 0;
> +}
> +
> +static struct regmap_bus regmap_gsc = {
> +	.reg_write = gsc_regmap_regwrite,
> +	.reg_read = gsc_regmap_regread,
> +};
> +
> +/*
> + * gsc_powerdown - API to use GSC to power down board for a specific time
> + *
> + * secs - number of seconds to remain powered off
> + */
> +static int gsc_powerdown(struct gsc_dev *gsc, unsigned long secs)
> +{
> +	int ret;
> +	unsigned char regs[4];
> +
> +	dev_info(&gsc->i2c->dev, "GSC powerdown for %ld seconds\n",
> +		 secs);
> +	regs[0] = secs & 0xff;
> +	regs[1] = (secs >> 8) & 0xff;
> +	regs[2] = (secs >> 16) & 0xff;
> +	regs[3] = (secs >> 24) & 0xff;
> +	ret = regmap_bulk_write(gsc->regmap, GSC_TIME_ADD, regs, 4);
> +
> +	return ret;
> +}
> +
> +/*
> + * sysfs hooks
> + */

This comment is superfluous since we know what _show & _store functions
do.

> +static ssize_t gsc_show(struct device *dev, struct device_attribute *attr,
> +			char *buf)
> +{
> +	struct gsc_dev *gsc = dev_get_drvdata(dev);
> +	const char *name = attr->attr.name;
> +	int rz = 0;
> +
> +	if (strcasecmp(name, "fw_version") == 0)
> +		rz = sprintf(buf, "%d\n", gsc->fwver);
> +	else if (strcasecmp(name, "fw_crc") == 0)
> +		rz = sprintf(buf, "0x%04x\n", gsc->fwcrc);
> +
> +	return rz;
> +}
> +
> +static ssize_t gsc_store(struct device *dev, struct device_attribute *attr,
> +			 const char *buf, size_t count)
> +{
> +	struct gsc_dev *gsc = dev_get_drvdata(dev);
> +	const char *name = attr->attr.name;
> +	int ret;
> +
> +	if (strcasecmp(name, "powerdown") == 0) {
> +		long value;
> +
> +		ret = kstrtol(buf, 0, &value);
> +		if (ret == 0)
> +			gsc_powerdown(gsc, value);
> +	} else
> +		dev_err(dev, "invalid name '%s\n", name);
> +
> +	return count;
> +}
> +
> +

Please remove 2nd '\n'.

> +/*
> + * Create a group of attributes so that we can create and destroy them all
> + * at once.
> + */

No need for this comment.

> +static struct device_attribute attr_fwver =
> +	__ATTR(fw_version, 0440, gsc_show, NULL);
> +static struct device_attribute attr_fwcrc =
> +	__ATTR(fw_crc, 0440, gsc_show, NULL);
> +static struct device_attribute attr_pwrdown =
> +	__ATTR(powerdown, 0220, NULL, gsc_store);
> +
> +static struct attribute *gsc_attrs[] = {
> +	&attr_fwver.attr,
> +	&attr_fwcrc.attr,
> +	&attr_pwrdown.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group attr_group = {
> +	.attrs = gsc_attrs,
> +};
> +
> +static const struct i2c_device_id gsc_i2c_ids[] = {
> +	{ "gsc_v1", gsc_v1 },
> +	{ "gsc_v2", gsc_v2 },
> +	{ "gsc_v3", gsc_v3 },
> +	{ },
> +};
> +
> +static const struct of_device_id gsc_of_match[] = {
> +	{ .compatible = "gw,gsc_v1", .data = (void *)gsc_v1 },
> +	{ .compatible = "gw,gsc_v2", .data = (void *)gsc_v2 },
> +	{ .compatible = "gw,gsc_v3", .data = (void *)gsc_v3 },
> +	{ }
> +};
> +
> +static const struct regmap_config gsc_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +	.cache_type = REGCACHE_NONE,
> +	.max_register = 0xf,
> +};
> +
> +static const struct regmap_config gsc_regmap_hwmon_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +	.cache_type = REGCACHE_NONE,
> +	.max_register = 0x37,
> +};
> +
> +static const struct regmap_irq gsc_irqs[] = {
> +	REGMAP_IRQ_REG(GSC_IRQ_PB, 0, BIT(GSC_IRQ_PB)),
> +	REGMAP_IRQ_REG(GSC_IRQ_KEY_ERASED, 0, BIT(GSC_IRQ_KEY_ERASED)),
> +	REGMAP_IRQ_REG(GSC_IRQ_EEPROM_WP, 0, BIT(GSC_IRQ_EEPROM_WP)),
> +	REGMAP_IRQ_REG(GSC_IRQ_RESV, 0, BIT(GSC_IRQ_RESV)),
> +	REGMAP_IRQ_REG(GSC_IRQ_GPIO, 0, BIT(GSC_IRQ_GPIO)),
> +	REGMAP_IRQ_REG(GSC_IRQ_TAMPER, 0, BIT(GSC_IRQ_TAMPER)),
> +	REGMAP_IRQ_REG(GSC_IRQ_WDT_TIMEOUT, 0, BIT(GSC_IRQ_WDT_TIMEOUT)),
> +	REGMAP_IRQ_REG(GSC_IRQ_SWITCH_HOLD, 0, BIT(GSC_IRQ_SWITCH_HOLD)),
> +};
> +
> +static const struct regmap_irq_chip gsc_irq_chip = {
> +	.name = KBUILD_MODNAME,

Please just type the name like "name".

> +	.irqs = gsc_irqs,
> +	.num_irqs = ARRAY_SIZE(gsc_irqs),
> +	.num_regs = 1,
> +	.status_base = GSC_IRQ_STATUS,
> +	.mask_base = GSC_IRQ_ENABLE,
> +	.mask_invert = true,
> +	.ack_base = GSC_IRQ_STATUS,
> +	.ack_invert = true,
> +};
> +
> +static int gsc_of_probe(struct device_node *np, struct gsc_dev *gsc)
> +{
> +	const struct of_device_id *of_id;
> +
> +	if (!np)
> +		return -ENODEV;
> +
> +	of_id = of_match_device(gsc_of_match, gsc->dev);
> +	if (of_id)
> +		gsc->type = (enum gsc_type)of_id->data;

Isn't there any way that you can fetch version information from the
device?

What is this value/information actually used for?

> +	return 0;
> +}
> +
> +static int
> +gsc_probe(struct i2c_client *client, const struct i2c_device_id *id)
> +{
> +	struct device *dev = &client->dev;
> +	struct gsc_dev *gsc;
> +	int ret;
> +	unsigned int reg;
> +
> +	gsc = devm_kzalloc(dev, sizeof(*gsc), GFP_KERNEL);
> +	if (!gsc)
> +		return -ENOMEM;
> +
> +	gsc->dev = &client->dev;
> +	gsc->i2c = client;
> +	gsc->irq = client->irq;
> +	i2c_set_clientdata(client, gsc);
> +
> +	gsc->regmap = devm_regmap_init(dev, &regmap_gsc, client,
> +				       &gsc_regmap_config);
> +	if (IS_ERR(gsc->regmap))
> +		return PTR_ERR(gsc->regmap);
> +
> +	ret = gsc_of_probe(dev->of_node, gsc);
> +	if (reg < 0)
> +		return ret;
> +
> +	if (regmap_read(gsc->regmap, GSC_FW_VER, &reg))
> +		return -EIO;
> +	gsc->fwver = reg;

'\n' here.

> +	regmap_read(gsc->regmap, GSC_FW_CRC, &reg);
> +	gsc->fwcrc = reg;
> +	regmap_read(gsc->regmap, GSC_FW_CRC + 1, &reg);
> +	gsc->fwcrc |= reg << 8;
> +
> +	gsc->i2c_hwmon = i2c_new_dummy(client->adapter, GSC_HWMON);
> +	if (!gsc->i2c_hwmon) {
> +		dev_err(dev, "Failed to allocate I2C device for HWMON\n");
> +		return -ENODEV;
> +	}
> +	i2c_set_clientdata(gsc->i2c_hwmon, gsc);
> +
> +	gsc->regmap_hwmon = devm_regmap_init(dev, &regmap_gsc, gsc->i2c_hwmon,
> +					     &gsc_regmap_hwmon_config);
> +	if (IS_ERR(gsc->regmap_hwmon)) {
> +		ret = PTR_ERR(gsc->regmap_hwmon);
> +		dev_err(dev, "failed to allocate register map: %d\n", ret);
> +		goto err_regmap;
> +	}
> +
> +	ret = devm_regmap_add_irq_chip(dev, gsc->regmap, gsc->irq,
> +				       IRQF_ONESHOT | IRQF_SHARED |
> +				       IRQF_TRIGGER_FALLING, 0,
> +				       &gsc_irq_chip, &gsc->irq_chip_data);
> +	if (ret)
> +		goto err_regmap;
> +
> +	dev_info(dev, "Gateworks System Controller v%d: fw v%02d 0x%04x\n",
> +		 gsc->type, gsc->fwver, gsc->fwcrc);
> +
> +	/* sysfs hooks */

Remove this comment please.

> +	ret = sysfs_create_group(&dev->kobj, &attr_group);
> +	if (ret)
> +		dev_err(dev, "failed to create sysfs attrs\n");
> +
> +	ret = of_platform_populate(dev->of_node, NULL, NULL, dev);
> +	if (ret)
> +		goto err_sysfs;
> +
> +	return 0;
> +
> +err_sysfs:
> +	sysfs_remove_group(&dev->kobj, &attr_group);
> +err_regmap:
> +	i2c_unregister_device(gsc->i2c_hwmon);
> +
> +	return ret;
> +}
> +
> +static int gsc_remove(struct i2c_client *client)
> +{
> +	sysfs_remove_group(&client->dev.kobj, &attr_group);

i2c_unregister_device()?

> +	return 0;
> +}
> +
> +static struct i2c_driver gsc_driver = {
> +	.driver = {
> +		.name	= KBUILD_MODNAME,

Just type the name please: "name".

> +		.of_match_table = of_match_ptr(gsc_of_match),
> +	},
> +	.probe		= gsc_probe,
> +	.remove		= gsc_remove,
> +	.id_table	= gsc_i2c_ids,
> +};
> +
> +module_i2c_driver(gsc_driver);
> +
> +MODULE_AUTHOR("Tim Harvey <tharvey@gateworks.com>");
> +MODULE_DESCRIPTION("I2C Core interface for GSC");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/mfd/gsc.h b/include/linux/mfd/gsc.h
> new file mode 100644
> index 0000000..e0d8c8f
> --- /dev/null
> +++ b/include/linux/mfd/gsc.h
> @@ -0,0 +1,82 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + *
> + * Copyright (C) 2018 Gateworks Corporation
> + */
> +#ifndef __LINUX_MFD_GSC_H_
> +#define __LINUX_MFD_GSC_H_
> +
> +/* Device Addresses */
> +#define GSC_MISC	0x20
> +#define GSC_UPDATE	0x21
> +#define GSC_GPIO	0x23
> +#define GSC_HWMON	0x29
> +#define GSC_EEPROM0	0x50
> +#define GSC_EEPROM1	0x51
> +#define GSC_EEPROM2	0x52
> +#define GSC_EEPROM3	0x53
> +#define GSC_RTC		0x68
> +
> +/* Register offsets */
> +#define GSC_CTRL_0	0x00
> +#define GSC_CTRL_1	0x01
> +#define GSC_TIME	0x02
> +#define GSC_TIME_ADD	0x06
> +#define GSC_IRQ_STATUS	0x0A
> +#define GSC_IRQ_ENABLE	0x0B
> +#define GSC_FW_CRC	0x0C
> +#define GSC_FW_VER	0x0E
> +#define GSC_WP		0x0F
> +
> +/* Bit definitions */
> +#define GSC_CTRL_0_PB_HARD_RESET	0
> +#define GSC_CTRL_0_PB_CLEAR_SECURE_KEY	1
> +#define GSC_CTRL_0_PB_SOFT_POWER_DOWN	2
> +#define GSC_CTRL_0_PB_BOOT_ALTERNATE	3
> +#define GSC_CTRL_0_PERFORM_CRC		4
> +#define GSC_CTRL_0_TAMPER_DETECT	5
> +#define GSC_CTRL_0_SWITCH_HOLD		6
> +
> +#define GSC_CTRL_1_SLEEP_ENABLE		0
> +#define GSC_CTRL_1_ACTIVATE_SLEEP	1
> +#define GSC_CTRL_1_LATCH_SLEEP_ADD	2
> +#define GSC_CTRL_1_SLEEP_NOWAKEPB	3
> +#define GSC_CTRL_1_WDT_TIME		4
> +#define GSC_CTRL_1_WDT_ENABLE		5
> +#define GSC_CTRL_1_SWITCH_BOOT_ENABLE	6
> +#define GSC_CTRL_1_SWITCH_BOOT_CLEAR	7
> +
> +#define GSC_IRQ_PB			0
> +#define GSC_IRQ_KEY_ERASED		1
> +#define GSC_IRQ_EEPROM_WP		2
> +#define GSC_IRQ_RESV			3
> +#define GSC_IRQ_GPIO			4
> +#define GSC_IRQ_TAMPER			5
> +#define GSC_IRQ_WDT_TIMEOUT		6
> +#define GSC_IRQ_SWITCH_HOLD		7
> +
> +/* Max registers */
> +#define GSC_HWMON_MAX_REG	56
> +
> +enum gsc_type {
> +	gsc_v1 = 1,
> +	gsc_v2 = 2,
> +	gsc_v3 = 3,
> +};
> +
> +struct gsc_dev {
> +	struct device *dev;
> +
> +	struct i2c_client *i2c;		/* 0x20: interrupt controller, WDT */
> +	struct i2c_client *i2c_hwmon;	/* 0x29: hwmon, fan controller */
> +
> +	struct regmap *regmap;
> +	struct regmap *regmap_hwmon;
> +	struct regmap_irq_chip_data *irq_chip_data;
> +
> +	int irq;
> +	enum gsc_type type;
> +	unsigned int fwver;
> +	unsigned short fwcrc;
> +};
> +
> +#endif /* __LINUX_MFD_GSC_H_ */
diff mbox

Patch

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 1d20a80..5694013 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -341,6 +341,19 @@  config MFD_EXYNOS_LPASS
 	  Select this option to enable support for Samsung Exynos Low Power
 	  Audio Subsystem.
 
+config MFD_GSC
+	tristate "Gateworks System Controller"
+	depends on (I2C && OF)
+	select MFD_CORE
+	select REGMAP_I2C
+	select REGMAP_IRQ
+	help
+	  Enable support for the Gateworks System Controller found
+	  on Gateworks Single Board Computers.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called gsc.
+
 config MFD_MC13XXX
 	tristate
 	depends on (SPI_MASTER || I2C)
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index d9474ad..aede0bc 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -18,6 +18,7 @@  obj-$(CONFIG_MFD_CROS_EC)	+= cros_ec_core.o
 obj-$(CONFIG_MFD_CROS_EC_I2C)	+= cros_ec_i2c.o
 obj-$(CONFIG_MFD_CROS_EC_SPI)	+= cros_ec_spi.o
 obj-$(CONFIG_MFD_EXYNOS_LPASS)	+= exynos-lpass.o
+obj-$(CONFIG_MFD_GSC)		+= gsc.o
 
 rtsx_pci-objs			:= rtsx_pcr.o rts5209.o rts5229.o rtl8411.o rts5227.o rts5249.o
 obj-$(CONFIG_MFD_RTSX_PCI)	+= rtsx_pci.o
diff --git a/drivers/mfd/gsc.c b/drivers/mfd/gsc.c
new file mode 100644
index 0000000..4ac400a
--- /dev/null
+++ b/drivers/mfd/gsc.c
@@ -0,0 +1,330 @@ 
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (C) 2018 Gateworks Corporation
+ *
+ * The Gateworks System Controller (GSC) is a family of a multi-function
+ * "Power Management and System Companion Device" chips originally designed for
+ * use in Gateworks Single Board Computers. The control interface is I2C,
+ * at 100kbps, with an interrupt.
+ *
+ */
+#include <linux/device.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/gsc.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+/*
+ * The GSC suffers from an errata where occasionally during
+ * ADC cycles the chip can NAK i2c transactions. To ensure we have reliable
+ * register access we place retries around register access.
+ */
+#define I2C_RETRIES	3
+
+static int gsc_regmap_regwrite(void *context, unsigned int reg,
+			       unsigned int val)
+{
+	struct i2c_client *client = context;
+	int retry, ret;
+
+	for (retry = 0; retry < I2C_RETRIES; retry++) {
+		ret = i2c_smbus_write_byte_data(client, reg, val);
+		/*
+		 * -EAGAIN returned when the i2c host controller is busy
+		 * -EIO returned when i2c device is busy
+		 */
+		if (ret != -EAGAIN && ret != -EIO)
+			break;
+	}
+	if (ret < 0) {
+		dev_err(&client->dev, ">> 0x%02x %d\n", reg, ret);
+		return ret;
+	}
+	dev_dbg(&client->dev, ">> 0x%02x=0x%02x (%d)\n", reg, val, retry);
+
+	return 0;
+}
+
+static int gsc_regmap_regread(void *context, unsigned int reg,
+			      unsigned int *val)
+{
+	struct i2c_client *client = context;
+	int retry, ret;
+
+	for (retry = 0; retry < I2C_RETRIES; retry++) {
+		ret = i2c_smbus_read_byte_data(client, reg);
+		/*
+		 * -EAGAIN returned when the i2c host controller is busy
+		 * -EIO returned when i2c device is busy
+		 */
+		if (ret != -EAGAIN && ret != -EIO)
+			break;
+	}
+	if (ret < 0) {
+		dev_err(&client->dev, "<< 0x%02x %d\n", reg, ret);
+		return ret;
+	}
+
+	*val = ret & 0xff;
+	dev_dbg(&client->dev, "<< 0x%02x=0x%02x (%d)\n", reg, *val, retry);
+
+	return 0;
+}
+
+static struct regmap_bus regmap_gsc = {
+	.reg_write = gsc_regmap_regwrite,
+	.reg_read = gsc_regmap_regread,
+};
+
+/*
+ * gsc_powerdown - API to use GSC to power down board for a specific time
+ *
+ * secs - number of seconds to remain powered off
+ */
+static int gsc_powerdown(struct gsc_dev *gsc, unsigned long secs)
+{
+	int ret;
+	unsigned char regs[4];
+
+	dev_info(&gsc->i2c->dev, "GSC powerdown for %ld seconds\n",
+		 secs);
+	regs[0] = secs & 0xff;
+	regs[1] = (secs >> 8) & 0xff;
+	regs[2] = (secs >> 16) & 0xff;
+	regs[3] = (secs >> 24) & 0xff;
+	ret = regmap_bulk_write(gsc->regmap, GSC_TIME_ADD, regs, 4);
+
+	return ret;
+}
+
+/*
+ * sysfs hooks
+ */
+static ssize_t gsc_show(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct gsc_dev *gsc = dev_get_drvdata(dev);
+	const char *name = attr->attr.name;
+	int rz = 0;
+
+	if (strcasecmp(name, "fw_version") == 0)
+		rz = sprintf(buf, "%d\n", gsc->fwver);
+	else if (strcasecmp(name, "fw_crc") == 0)
+		rz = sprintf(buf, "0x%04x\n", gsc->fwcrc);
+
+	return rz;
+}
+
+static ssize_t gsc_store(struct device *dev, struct device_attribute *attr,
+			 const char *buf, size_t count)
+{
+	struct gsc_dev *gsc = dev_get_drvdata(dev);
+	const char *name = attr->attr.name;
+	int ret;
+
+	if (strcasecmp(name, "powerdown") == 0) {
+		long value;
+
+		ret = kstrtol(buf, 0, &value);
+		if (ret == 0)
+			gsc_powerdown(gsc, value);
+	} else
+		dev_err(dev, "invalid name '%s\n", name);
+
+	return count;
+}
+
+
+/*
+ * Create a group of attributes so that we can create and destroy them all
+ * at once.
+ */
+static struct device_attribute attr_fwver =
+	__ATTR(fw_version, 0440, gsc_show, NULL);
+static struct device_attribute attr_fwcrc =
+	__ATTR(fw_crc, 0440, gsc_show, NULL);
+static struct device_attribute attr_pwrdown =
+	__ATTR(powerdown, 0220, NULL, gsc_store);
+
+static struct attribute *gsc_attrs[] = {
+	&attr_fwver.attr,
+	&attr_fwcrc.attr,
+	&attr_pwrdown.attr,
+	NULL,
+};
+
+static struct attribute_group attr_group = {
+	.attrs = gsc_attrs,
+};
+
+static const struct i2c_device_id gsc_i2c_ids[] = {
+	{ "gsc_v1", gsc_v1 },
+	{ "gsc_v2", gsc_v2 },
+	{ "gsc_v3", gsc_v3 },
+	{ },
+};
+
+static const struct of_device_id gsc_of_match[] = {
+	{ .compatible = "gw,gsc_v1", .data = (void *)gsc_v1 },
+	{ .compatible = "gw,gsc_v2", .data = (void *)gsc_v2 },
+	{ .compatible = "gw,gsc_v3", .data = (void *)gsc_v3 },
+	{ }
+};
+
+static const struct regmap_config gsc_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.cache_type = REGCACHE_NONE,
+	.max_register = 0xf,
+};
+
+static const struct regmap_config gsc_regmap_hwmon_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.cache_type = REGCACHE_NONE,
+	.max_register = 0x37,
+};
+
+static const struct regmap_irq gsc_irqs[] = {
+	REGMAP_IRQ_REG(GSC_IRQ_PB, 0, BIT(GSC_IRQ_PB)),
+	REGMAP_IRQ_REG(GSC_IRQ_KEY_ERASED, 0, BIT(GSC_IRQ_KEY_ERASED)),
+	REGMAP_IRQ_REG(GSC_IRQ_EEPROM_WP, 0, BIT(GSC_IRQ_EEPROM_WP)),
+	REGMAP_IRQ_REG(GSC_IRQ_RESV, 0, BIT(GSC_IRQ_RESV)),
+	REGMAP_IRQ_REG(GSC_IRQ_GPIO, 0, BIT(GSC_IRQ_GPIO)),
+	REGMAP_IRQ_REG(GSC_IRQ_TAMPER, 0, BIT(GSC_IRQ_TAMPER)),
+	REGMAP_IRQ_REG(GSC_IRQ_WDT_TIMEOUT, 0, BIT(GSC_IRQ_WDT_TIMEOUT)),
+	REGMAP_IRQ_REG(GSC_IRQ_SWITCH_HOLD, 0, BIT(GSC_IRQ_SWITCH_HOLD)),
+};
+
+static const struct regmap_irq_chip gsc_irq_chip = {
+	.name = KBUILD_MODNAME,
+	.irqs = gsc_irqs,
+	.num_irqs = ARRAY_SIZE(gsc_irqs),
+	.num_regs = 1,
+	.status_base = GSC_IRQ_STATUS,
+	.mask_base = GSC_IRQ_ENABLE,
+	.mask_invert = true,
+	.ack_base = GSC_IRQ_STATUS,
+	.ack_invert = true,
+};
+
+static int gsc_of_probe(struct device_node *np, struct gsc_dev *gsc)
+{
+	const struct of_device_id *of_id;
+
+	if (!np)
+		return -ENODEV;
+
+	of_id = of_match_device(gsc_of_match, gsc->dev);
+	if (of_id)
+		gsc->type = (enum gsc_type)of_id->data;
+
+	return 0;
+}
+
+static int
+gsc_probe(struct i2c_client *client, const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct gsc_dev *gsc;
+	int ret;
+	unsigned int reg;
+
+	gsc = devm_kzalloc(dev, sizeof(*gsc), GFP_KERNEL);
+	if (!gsc)
+		return -ENOMEM;
+
+	gsc->dev = &client->dev;
+	gsc->i2c = client;
+	gsc->irq = client->irq;
+	i2c_set_clientdata(client, gsc);
+
+	gsc->regmap = devm_regmap_init(dev, &regmap_gsc, client,
+				       &gsc_regmap_config);
+	if (IS_ERR(gsc->regmap))
+		return PTR_ERR(gsc->regmap);
+
+	ret = gsc_of_probe(dev->of_node, gsc);
+	if (reg < 0)
+		return ret;
+
+	if (regmap_read(gsc->regmap, GSC_FW_VER, &reg))
+		return -EIO;
+	gsc->fwver = reg;
+	regmap_read(gsc->regmap, GSC_FW_CRC, &reg);
+	gsc->fwcrc = reg;
+	regmap_read(gsc->regmap, GSC_FW_CRC + 1, &reg);
+	gsc->fwcrc |= reg << 8;
+
+	gsc->i2c_hwmon = i2c_new_dummy(client->adapter, GSC_HWMON);
+	if (!gsc->i2c_hwmon) {
+		dev_err(dev, "Failed to allocate I2C device for HWMON\n");
+		return -ENODEV;
+	}
+	i2c_set_clientdata(gsc->i2c_hwmon, gsc);
+
+	gsc->regmap_hwmon = devm_regmap_init(dev, &regmap_gsc, gsc->i2c_hwmon,
+					     &gsc_regmap_hwmon_config);
+	if (IS_ERR(gsc->regmap_hwmon)) {
+		ret = PTR_ERR(gsc->regmap_hwmon);
+		dev_err(dev, "failed to allocate register map: %d\n", ret);
+		goto err_regmap;
+	}
+
+	ret = devm_regmap_add_irq_chip(dev, gsc->regmap, gsc->irq,
+				       IRQF_ONESHOT | IRQF_SHARED |
+				       IRQF_TRIGGER_FALLING, 0,
+				       &gsc_irq_chip, &gsc->irq_chip_data);
+	if (ret)
+		goto err_regmap;
+
+	dev_info(dev, "Gateworks System Controller v%d: fw v%02d 0x%04x\n",
+		 gsc->type, gsc->fwver, gsc->fwcrc);
+
+	/* sysfs hooks */
+	ret = sysfs_create_group(&dev->kobj, &attr_group);
+	if (ret)
+		dev_err(dev, "failed to create sysfs attrs\n");
+
+	ret = of_platform_populate(dev->of_node, NULL, NULL, dev);
+	if (ret)
+		goto err_sysfs;
+
+	return 0;
+
+err_sysfs:
+	sysfs_remove_group(&dev->kobj, &attr_group);
+err_regmap:
+	i2c_unregister_device(gsc->i2c_hwmon);
+
+	return ret;
+}
+
+static int gsc_remove(struct i2c_client *client)
+{
+	sysfs_remove_group(&client->dev.kobj, &attr_group);
+
+	return 0;
+}
+
+static struct i2c_driver gsc_driver = {
+	.driver = {
+		.name	= KBUILD_MODNAME,
+		.of_match_table = of_match_ptr(gsc_of_match),
+	},
+	.probe		= gsc_probe,
+	.remove		= gsc_remove,
+	.id_table	= gsc_i2c_ids,
+};
+
+module_i2c_driver(gsc_driver);
+
+MODULE_AUTHOR("Tim Harvey <tharvey@gateworks.com>");
+MODULE_DESCRIPTION("I2C Core interface for GSC");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/mfd/gsc.h b/include/linux/mfd/gsc.h
new file mode 100644
index 0000000..e0d8c8f
--- /dev/null
+++ b/include/linux/mfd/gsc.h
@@ -0,0 +1,82 @@ 
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (C) 2018 Gateworks Corporation
+ */
+#ifndef __LINUX_MFD_GSC_H_
+#define __LINUX_MFD_GSC_H_
+
+/* Device Addresses */
+#define GSC_MISC	0x20
+#define GSC_UPDATE	0x21
+#define GSC_GPIO	0x23
+#define GSC_HWMON	0x29
+#define GSC_EEPROM0	0x50
+#define GSC_EEPROM1	0x51
+#define GSC_EEPROM2	0x52
+#define GSC_EEPROM3	0x53
+#define GSC_RTC		0x68
+
+/* Register offsets */
+#define GSC_CTRL_0	0x00
+#define GSC_CTRL_1	0x01
+#define GSC_TIME	0x02
+#define GSC_TIME_ADD	0x06
+#define GSC_IRQ_STATUS	0x0A
+#define GSC_IRQ_ENABLE	0x0B
+#define GSC_FW_CRC	0x0C
+#define GSC_FW_VER	0x0E
+#define GSC_WP		0x0F
+
+/* Bit definitions */
+#define GSC_CTRL_0_PB_HARD_RESET	0
+#define GSC_CTRL_0_PB_CLEAR_SECURE_KEY	1
+#define GSC_CTRL_0_PB_SOFT_POWER_DOWN	2
+#define GSC_CTRL_0_PB_BOOT_ALTERNATE	3
+#define GSC_CTRL_0_PERFORM_CRC		4
+#define GSC_CTRL_0_TAMPER_DETECT	5
+#define GSC_CTRL_0_SWITCH_HOLD		6
+
+#define GSC_CTRL_1_SLEEP_ENABLE		0
+#define GSC_CTRL_1_ACTIVATE_SLEEP	1
+#define GSC_CTRL_1_LATCH_SLEEP_ADD	2
+#define GSC_CTRL_1_SLEEP_NOWAKEPB	3
+#define GSC_CTRL_1_WDT_TIME		4
+#define GSC_CTRL_1_WDT_ENABLE		5
+#define GSC_CTRL_1_SWITCH_BOOT_ENABLE	6
+#define GSC_CTRL_1_SWITCH_BOOT_CLEAR	7
+
+#define GSC_IRQ_PB			0
+#define GSC_IRQ_KEY_ERASED		1
+#define GSC_IRQ_EEPROM_WP		2
+#define GSC_IRQ_RESV			3
+#define GSC_IRQ_GPIO			4
+#define GSC_IRQ_TAMPER			5
+#define GSC_IRQ_WDT_TIMEOUT		6
+#define GSC_IRQ_SWITCH_HOLD		7
+
+/* Max registers */
+#define GSC_HWMON_MAX_REG	56
+
+enum gsc_type {
+	gsc_v1 = 1,
+	gsc_v2 = 2,
+	gsc_v3 = 3,
+};
+
+struct gsc_dev {
+	struct device *dev;
+
+	struct i2c_client *i2c;		/* 0x20: interrupt controller, WDT */
+	struct i2c_client *i2c_hwmon;	/* 0x29: hwmon, fan controller */
+
+	struct regmap *regmap;
+	struct regmap *regmap_hwmon;
+	struct regmap_irq_chip_data *irq_chip_data;
+
+	int irq;
+	enum gsc_type type;
+	unsigned int fwver;
+	unsigned short fwcrc;
+};
+
+#endif /* __LINUX_MFD_GSC_H_ */