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    Subject[PATCH v8 3/7] mfd: Add base driver for Netronix embedded controller
    Date
    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>
    Acked-for-MFD-by: Lee Jones <lee.jones@linaro.org>
    ---
    v8:
    - Add missing MODULE_DEVICE_TABLE
    - Add module metadata (author, description, license)

    v7:
    - Add #define for version number (suggested by Lee Jones).

    v6:
    - https://lore.kernel.org/lkml/20201208011000.3060239-4-j.neuschaefer@gmx.net/
    - Add Lee Jones' ACK

    v5:
    - no changes

    v4:
    - https://lore.kernel.org/lkml/20201122222739.1455132-4-j.neuschaefer@gmx.net/
    - include asm/unaligned.h after linux/*
    - Use put_unaligned_be16 instead of open-coded big-endian packing
    - Clarify that 0x90=0xff00 causes an error in downstream kernel too
    - Add commas after non-sentinel positions
    - ntxec.h: declare structs device and regmap
    - Replace WARN_ON usage and add comments to explain errors
    - Replace dev_alert with dev_warn when the result isn't handled
    - Change subdevice registration error message to dev_err
    - Declare ntxec_reg8 as returning __be16
    - Restructure version detection code
    - Spell out ODM

    v3:
    - https://lore.kernel.org/lkml/20200924192455.2484005-4-j.neuschaefer@gmx.net/
    - 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@gmx.net/
    - 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 | 11 ++
    drivers/mfd/Makefile | 1 +
    drivers/mfd/ntxec.c | 221 ++++++++++++++++++++++++++++++++++++++
    include/linux/mfd/ntxec.h | 37 +++++++
    4 files changed, 270 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 bdfce7b156216..4280bcd47ec7d 100644
    --- a/drivers/mfd/Kconfig
    +++ b/drivers/mfd/Kconfig
    @@ -976,6 +976,17 @@ 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 14fdb188af022..948a3bf8e3e57 100644
    --- a/drivers/mfd/Makefile
    +++ b/drivers/mfd/Makefile
    @@ -219,6 +219,7 @@ 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
    index 0000000000000..9c435bcd9d88a
    --- /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 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;
    + }
    +
    + /* 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
    index 0000000000000..361204d125f1a
    --- /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
    --
    2.29.2
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