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Date:   Tue, 12 Jan 2021 20:36:49 +0100
From:   Andreas Kemnade <andreas@...nade.info>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>
Cc:     linux-kernel@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Sam Ravnborg <sam@...nborg.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Heiko Stuebner <heiko.stuebner@...obroma-systems.com>,
        Stephan Gerhold <stephan@...hold.net>,
        Lubomir Rintel <lkundrak@...sk>,
        Mark Brown <broonie@...nel.org>, allen <allen.chen@....com.tw>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        devicetree@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-rtc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Heiko Stuebner <heiko@...ech.de>,
        Josua Mayer <josua.mayer@....eu>,
        Arnd Bergmann <arnd@...db.de>, Daniel Palmer <daniel@...f.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v7 3/7] mfd: Add base driver for Netronix embedded
 controller

On Sat,  9 Jan 2021 19:02:16 +0100
Jonathan Neuschäfer <j.neuschaefer@....net> wrote:

> 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@....net>
> Acked-for-MFD-by: Lee Jones <lee.jones@...aro.org>
> ---
> 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       | 216 ++++++++++++++++++++++++++++++++++++++
>  include/linux/mfd/ntxec.h |  37 +++++++
>  4 files changed, 265 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..22ed2ef0669cb
> --- /dev/null
> +++ b/drivers/mfd/ntxec.c
> @@ -0,0 +1,216 @@
> +// 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@....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?

> +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_LICENSE()?

modpost moans about that here.

Regards,
Andreas

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