[RFC PATCH 04/10] mfd: Add base driver for Netronix embedded controller

["Jonathan Neuschäfer" <j.neuschaefer-hi6Y0CQ0nG0@public.gmane.org>]

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.

Known problems:
- The reboot handler is installed in such a way that it directly calls
  into the i2c subsystem to send the reboot command to the EC. This
  means that the reboot handler may sleep, which is not allowed.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer-hi6Y0CQ0nG0@public.gmane.org>
---
 drivers/mfd/Kconfig       |   7 ++
 drivers/mfd/Makefile      |   1 +
 drivers/mfd/ntxec.c       | 188 ++++++++++++++++++++++++++++++++++++++
 include/linux/mfd/ntxec.h |  30 ++++++
 4 files changed, 226 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 a37d7d1713820..78410b928648e 100644
--- 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
+	bool "Netronix Embedded Controller"
+	depends on I2C && OF
+	help
+	  Say yes here if you want to support the embedded controller of
+	  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 9367a92f795a6..19d9391ed6f32 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -218,6 +218,7 @@ 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..82adea34ea746
--- /dev/null
+++ b/drivers/mfd/ntxec.c
@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright 2020 Jonathan Neuschäfer
+//
+// MFD driver for the usually MSP430-based embedded controller used in certain
+// Netronix ebook reader board designs
+
+#include <asm/unaligned.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/i2c.h>
+#include <linux/mfd/ntxec.h>
+#include <linux/of_platform.h>
+#include <linux/pm.h>
+#include <linux/reboot.h>
+#include <linux/types.h>
+
+
+#define NTXEC_VERSION		0x00
+#define NTXEC_POWEROFF		0x50
+#define NTXEC_POWERKEEP		0x70
+#define NTXEC_RESET		0x90
+
+
+/* Register access */
+
+int ntxec_read16(struct ntxec *ec, u8 addr)
+{
+	u8 request[1] = { addr };
+	u8 response[2];
+	int res;
+
+	struct i2c_msg msgs[] = {
+		{
+			.addr = ec->client->addr,
+			.flags = ec->client->flags,
+			.len = sizeof(request),
+			.buf = request
+		}, {
+			.addr = ec->client->addr,
+			.flags = ec->client->flags | I2C_M_RD,
+			.len = sizeof(response),
+			.buf = response
+		}
+	};
+
+	res = i2c_transfer(ec->client->adapter, msgs, ARRAY_SIZE(msgs));
+	if (res < 0)
+		return res;
+	if (res != ARRAY_SIZE(msgs))
+		return -EIO;
+
+	return get_unaligned_be16(response);
+}
+EXPORT_SYMBOL(ntxec_read16);
+
+int ntxec_write16(struct ntxec *ec, u8 addr, u16 value)
+{
+	u8 request[3] = { addr, };
+	int res;
+
+	put_unaligned_be16(value, request + 1);
+
+	res = i2c_transfer_buffer_flags(ec->client, request, sizeof(request),
+					ec->client->flags);
+	if (res < 0)
+		return res;
+
+	return 0;
+}
+EXPORT_SYMBOL(ntxec_write16);
+
+int ntxec_read8(struct ntxec *ec, u8 addr)
+{
+	int res = ntxec_read16(ec, addr);
+
+	if (res < 0)
+		return res;
+
+	return (res >> 8) & 0xff;
+}
+EXPORT_SYMBOL(ntxec_read8);
+
+int ntxec_write8(struct ntxec *ec, u8 addr, u8 value)
+{
+	return ntxec_write16(ec, addr, value << 8);
+}
+EXPORT_SYMBOL(ntxec_write8);
+
+
+/* Reboot/poweroff handling */
+
+static struct ntxec *poweroff_restart_instance;
+
+static void ntxec_poweroff(void)
+{
+	ntxec_write8(poweroff_restart_instance, NTXEC_POWEROFF, 0x01);
+	msleep(5000);
+}
+
+static int ntxec_restart(struct notifier_block *nb,
+		unsigned long action, void *data)
+{
+	/* FIXME: The I2C driver sleeps, but restart handlers may not sleep */
+	ntxec_write8(poweroff_restart_instance, NTXEC_RESET, 0xff);
+	/* TODO: delay? */
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block ntxec_restart_handler = {
+	.notifier_call = ntxec_restart,
+	.priority = 128
+};
+
+
+/* Driver setup */
+
+static int ntxec_probe(struct i2c_client *client,
+			    const struct i2c_device_id *ids)
+{
+	struct ntxec *ec;
+	int res;
+
+	ec = devm_kmalloc(&client->dev, sizeof(*ec), GFP_KERNEL);
+	if (!ec)
+		return -ENOMEM;
+
+	ec->dev = &client->dev;
+	ec->client = client;
+
+	/* Determine the firmware version */
+	res = ntxec_read16(ec, NTXEC_VERSION);
+	if (res < 0) {
+		dev_dbg(ec->dev, "Failed to read firmware version number\n");
+		return res;
+	}
+	ec->version = res;
+
+	dev_info(ec->dev,
+		 "Netronix embedded controller version %04x detected.\n",
+		 ec->version);
+
+	/* For now, we don't support the new register layout. */
+	if (ntxec_has_new_layout(ec))
+		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 = ntxec_write8(ec, NTXEC_POWERKEEP, 0x08);
+		if (res < 0)
+			return res;
+
+		/* Install poweroff handler */
+		WARN_ON(poweroff_restart_instance);
+		poweroff_restart_instance = ec;
+		if (pm_power_off != NULL)
+			/* TODO: Refactor among all poweroff drivers */
+			dev_err(ec->dev, "pm_power_off already assigned\n");
+		else
+			pm_power_off = ntxec_poweroff;
+
+		/* Install board reset handler */
+		res = register_restart_handler(&ntxec_restart_handler);
+		if (res < 0)
+			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 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		= ntxec_probe,
+};
+builtin_i2c_driver(ntxec_driver);
diff --git a/include/linux/mfd/ntxec.h b/include/linux/mfd/ntxec.h
new file mode 100644
index 0000000000000..9f9d6f2141751
--- /dev/null
+++ b/include/linux/mfd/ntxec.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2020 Jonathan Neuschäfer
+ *
+ * MFD access functions for the Netronix embedded controller.
+ */
+
+#ifndef NTXEC_H
+#define NTXEC_H
+
+#include <linux/types.h>
+
+struct ntxec {
+	struct device *dev;
+	struct i2c_client *client;
+	u16 version;
+	/* TODO: Add a mutex to protect actions consisting of multiple accesses? */
+};
+
+static inline bool ntxec_has_new_layout(struct ntxec *ec)
+{
+	return ec->version == 0xe916;
+}
+
+int ntxec_read16(struct ntxec *ec, u8 addr);
+int ntxec_write16(struct ntxec *ec, u8 addr, u16 value);
+int ntxec_read8(struct ntxec *ec, u8 addr);
+int ntxec_write8(struct ntxec *ec, u8 addr, u8 value);
+
+#endif
--
2.27.0