mfd: Add base driver for Netronix embedded controller

The Netronix embedded controller is a microcontroller found in some
e-book readers designed by the original design manufacturer 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@gmx.net>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index b74efa4..a03de3f 100644 (file)
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -967,6 +967,17 @@ 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 original design manufacturer
+         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 834f546..bb5e8f2 100644 (file)
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -218,6 +218,7 @@ obj-$(CONFIG_MFD_INTEL_PMC_BXT)     += intel_pmc_bxt.o
 obj-$(CONFIG_MFD_INTEL_PMT)    += intel_pmt.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 (file)
index 0000000..957de2b
--- /dev/null
+++ b/drivers/mfd/ntxec.c
@@ -0,0 +1,221 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * The Netronix embedded controller is a microcontroller found in some
+ * e-book readers designed by the original design manufacturer 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@gmx.net>
+ */
+
+#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>
+#include <asm/unaligned.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[3] = { NTXEC_REG_POWEROFF };
+       struct i2c_msg msgs[] = {
+               {
+                       .addr = poweroff_restart_client->addr,
+                       .flags = 0,
+                       .len = sizeof(buf),
+                       .buf = buf,
+               },
+       };
+
+       put_unaligned_be16(NTXEC_POWEROFF_VALUE, buf + 1);
+
+       res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
+       if (res < 0)
+               dev_warn(&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;
+       u8 buf[3] = { NTXEC_REG_RESET };
+       /*
+        * NOTE: The lower half of the reset value is not sent, because sending
+        * it causes an I2C error. (The reset handler in the downstream driver
+        * does send the full two-byte value, but doesn't check the result).
+        */
+       struct i2c_msg msgs[] = {
+               {
+                       .addr = poweroff_restart_client->addr,
+                       .flags = 0,
+                       .len = sizeof(buf) - 1,
+                       .buf = buf,
+               },
+       };
+
+       put_unaligned_be16(NTXEC_RESET_VALUE, buf + 1);
+
+       res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
+       if (res < 0)
+               dev_warn(&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 PTR_ERR(ec->regmap);
+       }
+
+       /* 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;
+       }
+
+       /* Bail out if we encounter an unknown firmware version */
+       switch (version) {
+       case NTXEC_VERSION_KOBO_AURA:
+               break;
+       default:
+               dev_err(ec->dev,
+                       "Netronix embedded controller version %04x is not supported.\n",
+                       version);
+               return -ENODEV;
+       }
+
+       dev_info(ec->dev,
+                "Netronix embedded controller version %04x detected.\n", version);
+
+       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;
+
+               if (poweroff_restart_client)
+                       /*
+                        * Another instance of the driver already took
+                        * poweroff/restart duties.
+                        */
+                       dev_err(ec->dev, "poweroff_restart_client already assigned\n");
+               else
+                       poweroff_restart_client = client;
+
+               if (pm_power_off)
+                       /* Another driver already registered a poweroff handler. */
+                       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_err(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", },
+       {}
+};
+MODULE_DEVICE_TABLE(of, of_ntxec_match_table);
+
+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);
+
+MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@gmx.net>");
+MODULE_DESCRIPTION("Core driver for Netronix EC");
+MODULE_LICENSE("GPL");

diff --git a/include/linux/mfd/ntxec.h b/include/linux/mfd/ntxec.h
new file mode 100644 (file)
index 0000000..361204d
--- /dev/null
+++ b/include/linux/mfd/ntxec.h
@@ -0,0 +1,37 @@
+/* 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 device;
+struct regmap;
+
+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 __be16 ntxec_reg8(u8 value)
+{
+       return value << 8;
+}
+
+/* Known firmware versions */
+#define NTXEC_VERSION_KOBO_AURA        0xd726  /* found in Kobo Aura */
+
+#endif