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        linux-rtc@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
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Subject: [PATCH v2 03/10] mfd: Add base driver for Netronix embedded controller
Date:   Sat,  5 Sep 2020 15:32:23 +0200
Message-Id: <20200905133230.1014581-4-j.neuschaefer@gmx.net>
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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-contr=
oller

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

Signed-off-by: Jonathan Neusch=C3=A4fer <j.neuschaefer@gmx.net>
=2D--

v2:
- 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 control=
ler'
  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 sa=
fe")
- 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 =3D signs in struct initializers [Uwe Kleine-K=C3=B6nig]
- 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
=2D--
 drivers/mfd/Kconfig       |   7 ++
 drivers/mfd/Makefile      |   1 +
 drivers/mfd/ntxec.c       | 217 ++++++++++++++++++++++++++++++++++++++
 include/linux/mfd/ntxec.h |  24 +++++
 4 files changed, 249 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..bab999081f32d 100644
=2D-- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -978,6 +978,13 @@ 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"
+	depends on I2C && OF
+	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
=2D-- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -217,6 +217,7 @@ obj-$(CONFIG_MFD_INTEL_MSIC)	+=3D intel_msic.o
 obj-$(CONFIG_MFD_INTEL_PMC_BXT)	+=3D intel_pmc_bxt.o
 obj-$(CONFIG_MFD_PALMAS)	+=3D palmas.o
 obj-$(CONFIG_MFD_VIPERBOARD)    +=3D viperboard.o
+obj-$(CONFIG_MFD_NTXEC)		+=3D ntxec.o
 obj-$(CONFIG_MFD_RC5T583)	+=3D rc5t583.o rc5t583-irq.o
 obj-$(CONFIG_MFD_RK808)		+=3D rk808.o
 obj-$(CONFIG_MFD_RN5T618)	+=3D rn5t618.o
diff --git a/drivers/mfd/ntxec.c b/drivers/mfd/ntxec.c
new file mode 100644
index 0000000000000..49cc4fa35b9fe
=2D-- /dev/null
+++ b/drivers/mfd/ntxec.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * 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 Neusch=C3=A4fer
+ */
+
+#include <asm/unaligned.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/i2c.h>
+#include <linux/mfd/ntxec.h>
+#include <linux/module.h>
+#include <linux/of_platform.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[] =3D {
+		NTXEC_REG_POWEROFF,
+		(NTXEC_POWEROFF_VALUE >> 8) & 0xff,
+		NTXEC_POWEROFF_VALUE & 0xff,
+	};
+
+	struct i2c_msg msgs[] =3D {
+		{
+			.addr =3D poweroff_restart_client->addr,
+			.flags =3D 0,
+			.len =3D sizeof(buf),
+			.buf =3D buf
+		}
+	};
+
+	res =3D i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(=
msgs));
+
+	if (res < 0)
+		dev_alert(&poweroff_restart_client->dev, "Failed to power off (err =3D =
%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[] =3D {
+		NTXEC_REG_RESET,
+		(NTXEC_RESET_VALUE >> 8) & 0xff,
+	};
+
+	struct i2c_msg msgs[] =3D {
+		{
+			.addr =3D poweroff_restart_client->addr,
+			.flags =3D 0,
+			.len =3D sizeof(buf),
+			.buf =3D buf
+		}
+	};
+
+	res =3D i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(=
msgs));
+
+	if (res < 0)
+		dev_alert(&poweroff_restart_client->dev, "Failed to restart (err =3D %d=
)\n", res);
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block ntxec_restart_handler =3D {
+	.notifier_call =3D ntxec_restart,
+	.priority =3D 128
+};
+
+static const struct regmap_config regmap_config =3D {
+	.name =3D "ntxec",
+	.reg_bits =3D 8,
+	.val_bits =3D 16,
+	.cache_type =3D REGCACHE_NONE,
+	.val_format_endian =3D REGMAP_ENDIAN_BIG,
+};
+
+static const struct ntxec_info ntxec_known_versions[] =3D {
+	{ 0xd726 }, /* found in Kobo Aura */
+};
+
+static const struct ntxec_info *ntxec_lookup_info(u16 version)
+{
+	int i;
+
+	for (i =3D 0; i < ARRAY_SIZE(ntxec_known_versions); i++) {
+		const struct ntxec_info *info =3D &ntxec_known_versions[i];
+
+		if (info->version =3D=3D version)
+			return info;
+	}
+
+	return NULL;
+}
+
+static int ntxec_probe(struct i2c_client *client)
+{
+	struct ntxec *ec;
+	unsigned int version;
+	int res;
+
+	ec =3D devm_kmalloc(&client->dev, sizeof(*ec), GFP_KERNEL);
+	if (!ec)
+		return -ENOMEM;
+
+	ec->dev =3D &client->dev;
+
+	ec->regmap =3D 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 =3D 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 */
+	ec->info =3D ntxec_lookup_info(version);
+	if (!ec->info)
+		return -EOPNOTSUPP;
+
+	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 =3D regmap_write(ec->regmap, NTXEC_REG_POWERKEEP,
+				   NTXEC_POWERKEEP_VALUE);
+		if (res < 0)
+			return res;
+
+		/* Install poweroff handler */
+		WARN_ON(poweroff_restart_client);
+		poweroff_restart_client =3D client;
+		if (pm_power_off)
+			dev_err(ec->dev, "pm_power_off already assigned\n");
+		else
+			pm_power_off =3D ntxec_poweroff;
+
+		/* Install board reset handler */
+		res =3D 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);
+
+	return devm_of_platform_populate(ec->dev);
+}
+
+static int ntxec_remove(struct i2c_client *i2c)
+{
+	if (i2c =3D=3D poweroff_restart_client) {
+		poweroff_restart_client =3D NULL;
+		pm_power_off =3D NULL;
+		unregister_restart_handler(&ntxec_restart_handler);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id of_ntxec_match_table[] =3D {
+	{ .compatible =3D "netronix,ntxec", },
+	{}
+};
+
+static struct i2c_driver ntxec_driver =3D {
+	.driver =3D {
+		.name =3D "ntxec",
+		.of_match_table =3D of_ntxec_match_table,
+	},
+	.probe_new =3D ntxec_probe,
+	.remove =3D 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..65e389af79da6
=2D-- /dev/null
+++ b/include/linux/mfd/ntxec.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2020 Jonathan Neusch=C3=A4fer
+ *
+ * Register access and version information for the Netronix embedded
+ * controller.
+ */
+
+#ifndef NTXEC_H
+#define NTXEC_H
+
+#include <linux/types.h>
+
+struct ntxec_info {
+	u16 version;
+};
+
+struct ntxec {
+	struct device *dev;
+	struct regmap *regmap;
+	const struct ntxec_info *info;
+};
+
+#endif
=2D-
2.28.0