[PATCH v3 3/7] mfd: Add base driver for Netronix embedded controller

[Jonathan Neuschäfer]

The Netronix embedded controller is a microcontroller found in some
e-book readers designed by the ODM Netronix, Inc. It contains RTC,
battery monitoring, system power management, and PWM functionality.

This driver implements register access and version detection.

Third-party hardware documentation is available at:

  https://github.com/neuschaefer/linux/wiki/Netronix-MSP430-embedded-controller

The EC supports interrupts, but the driver doesn't make use of them so
far.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@xxxxxxx>
---

v3:
- Add (EC) to CONFIG_MFD_NTXEC prompt
- Relicense as GPLv2 or later
- Add email address to copyright line
- remove empty lines in ntxec_poweroff and ntxec_restart functions
- Split long lines
- Remove 'Install ... handler' comments
- Make naming of struct i2c_client parameter consistent
- Remove struct ntxec_info
- Rework 'depends on' lines in Kconfig, hard-depend on I2C, select REGMAP_I2C and
  MFD_CORE
- Register subdevices via mfd_cells
- Move 8-bit register conversion to ntxec.h

v2:
- https://lore.kernel.org/lkml/20200905133230.1014581-4-j.neuschaefer@xxxxxxx/
- Add a description of the device to the patch text
- Unify spelling as 'Netronix embedded controller'.
  'Netronix' is the proper name of the manufacturer, but 'embedded controller'
  is just a label that I have assigned to the device.
- Switch to regmap, avoid regmap use in poweroff and reboot handlers.
  Inspired by cf84dc0bb40f4 ("mfd: rn5t618: Make restart handler atomic safe")
- Use a list of known-working firmware versions instead of checking for a
  known-incompatible version
- Prefix registers with NTXEC_REG_
- Define register values as constants
- Various style cleanups as suggested by Lee Jones
- Don't align = signs in struct initializers [Uwe Kleine-König]
- Don't use dev_dbg for an error message
- Explain sleep in poweroff handler
- Remove (struct ntxec).client
- Switch to .probe_new in i2c driver
- Add .remove callback
- Make CONFIG_MFD_NTXEC a tristate option
---
 drivers/mfd/Kconfig       |  10 ++
 drivers/mfd/Makefile      |   1 +
 drivers/mfd/ntxec.c       | 206 ++++++++++++++++++++++++++++++++++++++
 include/linux/mfd/ntxec.h |  31 ++++++
 4 files changed, 248 insertions(+)
 create mode 100644 drivers/mfd/ntxec.c
 create mode 100644 include/linux/mfd/ntxec.h

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 33df0837ab415..b313103151508 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -978,6 +978,16 @@ config MFD_VIPERBOARD
 	  You need to select the mfd cell drivers separately.
 	  The drivers do not support all features the board exposes.

+config MFD_NTXEC
+	tristate "Netronix embedded controller (EC)"
+	depends on OF || COMPILE_TEST
+	depends on I2C
+	select REGMAP_I2C
+	select MFD_CORE
+	help
+	  Say yes here if you want to support the embedded controller found in
+	  certain e-book readers designed by the ODM Netronix.
+
 config MFD_RETU
 	tristate "Nokia Retu and Tahvo multi-function device"
 	select MFD_CORE
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index a60e5f835283e..236a8acd917a0 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -217,6 +217,7 @@ obj-$(CONFIG_MFD_INTEL_MSIC)	+= intel_msic.o
 obj-$(CONFIG_MFD_INTEL_PMC_BXT)	+= intel_pmc_bxt.o
 obj-$(CONFIG_MFD_PALMAS)	+= palmas.o
 obj-$(CONFIG_MFD_VIPERBOARD)    += viperboard.o
+obj-$(CONFIG_MFD_NTXEC)		+= ntxec.o
 obj-$(CONFIG_MFD_RC5T583)	+= rc5t583.o rc5t583-irq.o
 obj-$(CONFIG_MFD_RK808)		+= rk808.o
 obj-$(CONFIG_MFD_RN5T618)	+= rn5t618.o
diff --git a/drivers/mfd/ntxec.c b/drivers/mfd/ntxec.c
new file mode 100644
index 0000000000000..93611b85a32e0
--- /dev/null
+++ b/drivers/mfd/ntxec.c
@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * The Netronix embedded controller is a microcontroller found in some
+ * e-book readers designed by the ODM Netronix, Inc. It contains RTC,
+ * battery monitoring, system power management, and PWM functionality.
+ *
+ * This driver implements register access, version detection, and system
+ * power-off/reset.
+ *
+ * Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@xxxxxxx>
+ */
+
+#include <asm/unaligned.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/i2c.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/ntxec.h>
+#include <linux/module.h>
+#include <linux/pm.h>
+#include <linux/reboot.h>
+#include <linux/regmap.h>
+#include <linux/types.h>
+
+#define NTXEC_REG_VERSION	0x00
+#define NTXEC_REG_POWEROFF	0x50
+#define NTXEC_REG_POWERKEEP	0x70
+#define NTXEC_REG_RESET		0x90
+
+#define NTXEC_POWEROFF_VALUE	0x0100
+#define NTXEC_POWERKEEP_VALUE	0x0800
+#define NTXEC_RESET_VALUE	0xff00
+
+static struct i2c_client *poweroff_restart_client;
+
+static void ntxec_poweroff(void)
+{
+	int res;
+	u8 buf[] = {
+		NTXEC_REG_POWEROFF,
+		(NTXEC_POWEROFF_VALUE >> 8) & 0xff,
+		NTXEC_POWEROFF_VALUE & 0xff,
+	};
+	struct i2c_msg msgs[] = {
+		{
+			.addr = poweroff_restart_client->addr,
+			.flags = 0,
+			.len = sizeof(buf),
+			.buf = buf
+		}
+	};
+
+	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
+	if (res < 0)
+		dev_alert(&poweroff_restart_client->dev,
+			  "Failed to power off (err = %d)\n", res);
+
+	/*
+	 * The time from the register write until the host CPU is powered off
+	 * has been observed to be about 2.5 to 3 seconds. Sleep long enough to
+	 * safely avoid returning from the poweroff handler.
+	 */
+	msleep(5000);
+}
+
+static int ntxec_restart(struct notifier_block *nb,
+			 unsigned long action, void *data)
+{
+	int res;
+	/*
+	 * NOTE: The lower half of the reset value is not sent, because sending
+	 * it causes an error
+	 */
+	u8 buf[] = {
+		NTXEC_REG_RESET,
+		(NTXEC_RESET_VALUE >> 8) & 0xff,
+	};
+	struct i2c_msg msgs[] = {
+		{
+			.addr = poweroff_restart_client->addr,
+			.flags = 0,
+			.len = sizeof(buf),
+			.buf = buf
+		}
+	};
+
+	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
+	if (res < 0)
+		dev_alert(&poweroff_restart_client->dev,
+			  "Failed to restart (err = %d)\n", res);
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block ntxec_restart_handler = {
+	.notifier_call = ntxec_restart,
+	.priority = 128
+};
+
+static const struct regmap_config regmap_config = {
+	.name = "ntxec",
+	.reg_bits = 8,
+	.val_bits = 16,
+	.cache_type = REGCACHE_NONE,
+	.val_format_endian = REGMAP_ENDIAN_BIG,
+};
+
+static const struct mfd_cell ntxec_subdevices[] = {
+	{ .name = "ntxec-rtc" },
+	{ .name = "ntxec-pwm" },
+};
+
+static int ntxec_probe(struct i2c_client *client)
+{
+	struct ntxec *ec;
+	unsigned int version;
+	int res;
+
+	ec = devm_kmalloc(&client->dev, sizeof(*ec), GFP_KERNEL);
+	if (!ec)
+		return -ENOMEM;
+
+	ec->dev = &client->dev;
+
+	ec->regmap = devm_regmap_init_i2c(client, &regmap_config);
+	if (IS_ERR(ec->regmap)) {
+		dev_err(ec->dev, "Failed to set up regmap for device\n");
+		return res;
+	}
+
+	/* Determine the firmware version */
+	res = regmap_read(ec->regmap, NTXEC_REG_VERSION, &version);
+	if (res < 0) {
+		dev_err(ec->dev, "Failed to read firmware version number\n");
+		return res;
+	}
+	dev_info(ec->dev,
+		 "Netronix embedded controller version %04x detected.\n",
+		 version);
+
+	/* Bail out if we encounter an unknown firmware version */
+	switch (version) {
+	case 0xd726: /* found in Kobo Aura */
+		break;
+	default:
+		return -ENODEV;
+	}
+
+	if (of_device_is_system_power_controller(ec->dev->of_node)) {
+		/*
+		 * Set the 'powerkeep' bit. This is necessary on some boards
+		 * in order to keep the system running.
+		 */
+		res = regmap_write(ec->regmap, NTXEC_REG_POWERKEEP,
+				   NTXEC_POWERKEEP_VALUE);
+		if (res < 0)
+			return res;
+
+		WARN_ON(poweroff_restart_client);
+		poweroff_restart_client = client;
+		if (pm_power_off)
+			dev_err(ec->dev, "pm_power_off already assigned\n");
+		else
+			pm_power_off = ntxec_poweroff;
+
+		res = register_restart_handler(&ntxec_restart_handler);
+		if (res)
+			dev_err(ec->dev,
+				"Failed to register restart handler: %d\n", res);
+	}
+
+	i2c_set_clientdata(client, ec);
+
+	res = devm_mfd_add_devices(ec->dev, PLATFORM_DEVID_NONE, ntxec_subdevices,
+				   ARRAY_SIZE(ntxec_subdevices), NULL, 0, NULL);
+	if (res)
+		dev_warn(ec->dev, "Failed to add subdevices: %d\n", res);
+
+	return res;
+}
+
+static int ntxec_remove(struct i2c_client *client)
+{
+	if (client == poweroff_restart_client) {
+		poweroff_restart_client = NULL;
+		pm_power_off = NULL;
+		unregister_restart_handler(&ntxec_restart_handler);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id of_ntxec_match_table[] = {
+	{ .compatible = "netronix,ntxec", },
+	{}
+};
+
+static struct i2c_driver ntxec_driver = {
+	.driver = {
+		.name = "ntxec",
+		.of_match_table = of_ntxec_match_table,
+	},
+	.probe_new = ntxec_probe,
+	.remove = ntxec_remove,
+};
+module_i2c_driver(ntxec_driver);
diff --git a/include/linux/mfd/ntxec.h b/include/linux/mfd/ntxec.h
new file mode 100644
index 0000000000000..a39c85978f61b
--- /dev/null
+++ b/include/linux/mfd/ntxec.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2020 Jonathan Neuschäfer
+ *
+ * Register access and version information for the Netronix embedded
+ * controller.
+ */
+
+#ifndef NTXEC_H
+#define NTXEC_H
+
+#include <linux/types.h>
+
+struct ntxec {
+	struct device *dev;
+	struct regmap *regmap;
+};
+
+/*
+ * Some registers, such as the battery status register (0x41), are in
+ * big-endian, but others only have eight significant bits, which are in the
+ * first byte transmitted over I2C (the MSB of the big-endian value).
+ * This convenience function converts an 8-bit value to 16-bit for use in the
+ * second kind of register.
+ */
+static inline u16 ntxec_reg8(u8 value)
+{
+	return value << 8;
+}
+
+#endif
--
2.28.0