mfd: ene-kb3930: Add driver for ENE KB3930 Embedded Controller

This driver provides access to the EC RAM of said embedded controller
attached to the I2C bus as well as optionally supporting its slightly weird
power-off/restart protocol.

A particular implementation of the EC firmware can be identified by a
model byte. If this driver identifies the Dell Ariel platform, it
registers the appropriate cells.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

3 files changed, 224 insertions, 0 deletions

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 4b918fdcc7c7..e1d3bf77b245 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -398,6 +398,17 @@ config MFD_DLN2
 	  etc. must be enabled in order to use the functionality of
 	  the device.
 
+config MFD_ENE_KB3930
+	tristate "ENE KB3930 Embedded Controller support"
+	depends on I2C
+	depends on MACH_MMP3_DT || COMPILE_TEST
+	select MFD_CORE
+	help
+	  This adds support for the power-off functionality and access to
+	  the registers that control LEDS and USB port power on ENE KB3930
+	  Embedded Controller. To use the LED functionality LEDS_ARIEL must
+	  be enabled.
+
 config MFD_EXYNOS_LPASS
 	tristate "Samsung Exynos SoC Low Power Audio Subsystem"
 	depends on ARCH_EXYNOS || COMPILE_TEST
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index 78d24a3e7c9e..e6c7520ed129 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -14,6 +14,7 @@ obj-$(CONFIG_ARCH_BCM2835)	+= bcm2835-pm.o
 obj-$(CONFIG_MFD_BCM590XX)	+= bcm590xx.o
 obj-$(CONFIG_MFD_BD9571MWV)	+= bd9571mwv.o
 obj-$(CONFIG_MFD_CROS_EC_DEV)	+= cros_ec_dev.o
+obj-$(CONFIG_MFD_ENE_KB3930)	+= ene-kb3930.o
 obj-$(CONFIG_MFD_EXYNOS_LPASS)	+= exynos-lpass.o
 obj-$(CONFIG_MFD_GATEWORKS_GSC)	+= gateworks-gsc.o
 
diff --git a/drivers/mfd/ene-kb3930.c b/drivers/mfd/ene-kb3930.c
new file mode 100644
index 000000000000..1c32ff586816
--- /dev/null
+++ b/drivers/mfd/ene-kb3930.c
@@ -0,0 +1,212 @@
+// SPDX-License-Identifier: BSD-2-Clause OR GPL-2.0-or-later
+/*
+ * ENE KB3930 Embedded Controller Driver
+ *
+ * Copyright (C) 2020 Lubomir Rintel
+ */
+
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/mfd/core.h>
+#include <linux/module.h>
+#include <linux/reboot.h>
+#include <linux/regmap.h>
+
+/* I2C registers that are multiplexing access to the EC RAM. */
+enum {
+	EC_DATA_IN	= 0x00,
+	EC_RAM_OUT	= 0x80,
+	EC_RAM_IN	= 0x81,
+};
+
+/* EC RAM registers. */
+enum {
+	EC_MODEL	= 0x30,
+	EC_VERSION_MAJ	= 0x31,
+	EC_VERSION_MIN	= 0x32,
+};
+
+struct kb3930 {
+	struct i2c_client *client;
+	struct regmap *ram_regmap;
+	struct gpio_descs *off_gpios;
+};
+
+struct kb3930 *kb3930_power_off;
+
+#define EC_GPIO_WAVE		0
+#define EC_GPIO_OFF_MODE	1
+
+#define EC_OFF_MODE_REBOOT	0
+#define EC_OFF_MODE_POWER	1
+
+static void kb3930_off(struct kb3930 *ddata, int off_mode)
+{
+	gpiod_direction_output(ddata->off_gpios->desc[EC_GPIO_OFF_MODE],
+			       off_mode);
+
+	/*
+	 * This creates a 10 Hz wave on EC_GPIO_WAVE that signals a
+	 * shutdown request to the EC. Once the EC detects it, it will
+	 * proceed to turn the power off or reset the board depending on
+	 * the value of EC_GPIO_OFF_MODE.
+	 */
+	while (1) {
+		mdelay(50);
+		gpiod_direction_output(ddata->off_gpios->desc[EC_GPIO_WAVE], 0);
+		mdelay(50);
+		gpiod_direction_output(ddata->off_gpios->desc[EC_GPIO_WAVE], 1);
+	}
+}
+
+static int kb3930_restart(struct notifier_block *this,
+			  unsigned long mode, void *cmd)
+{
+	kb3930_off(kb3930_power_off, EC_OFF_MODE_REBOOT);
+	return NOTIFY_DONE;
+}
+
+static void kb3930_pm_power_off(void)
+{
+	kb3930_off(kb3930_power_off, EC_OFF_MODE_POWER);
+}
+
+static struct notifier_block kb3930_restart_nb = {
+	.notifier_call = kb3930_restart,
+};
+
+static const struct mfd_cell ariel_ec_cells[] = {
+	{ .name = "dell-wyse-ariel-led", },
+	{ .name = "dell-wyse-ariel-power", },
+};
+
+static int kb3930_ec_ram_reg_write(void *context, unsigned int reg,
+				   unsigned int val)
+{
+	struct kb3930 *ddata = context;
+
+	return i2c_smbus_write_word_data(ddata->client, EC_RAM_OUT,
+					 (val << 8) | reg);
+}
+
+static int kb3930_ec_ram_reg_read(void *context, unsigned int reg,
+				  unsigned int *val)
+{
+	struct kb3930 *ddata = context;
+	int ret;
+
+	ret = i2c_smbus_write_word_data(ddata->client, EC_RAM_IN, reg);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_read_word_data(ddata->client, EC_DATA_IN);
+	if (ret < 0)
+		return ret;
+
+	*val = ret >> 8;
+	return 0;
+}
+
+static const struct regmap_config kb3930_ram_regmap_config = {
+	.name = "ec_ram",
+	.reg_bits = 8,
+	.val_bits = 8,
+	.reg_stride = 1,
+	.max_register = 0xff,
+	.reg_write = kb3930_ec_ram_reg_write,
+	.reg_read = kb3930_ec_ram_reg_read,
+	.fast_io = false,
+};
+
+static int kb3930_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct device_node *np = dev->of_node;
+	struct kb3930 *ddata;
+	unsigned int model;
+	int ret;
+
+	ddata = devm_kzalloc(dev, sizeof(*ddata), GFP_KERNEL);
+	if (!ddata)
+		return -ENOMEM;
+
+	kb3930_power_off = ddata;
+	ddata->client = client;
+	i2c_set_clientdata(client, ddata);
+
+	ddata->ram_regmap = devm_regmap_init(dev, NULL, ddata,
+					     &kb3930_ram_regmap_config);
+	if (IS_ERR(ddata->ram_regmap))
+		return PTR_ERR(ddata->ram_regmap);
+
+	ret = regmap_read(ddata->ram_regmap, EC_MODEL, &model);
+	if (ret < 0)
+		return ret;
+
+	/* Currently we only support the cells present on Dell Ariel model. */
+	if (model != 'J') {
+		dev_err(dev, "unknown board model: %02x\n", model);
+		return -ENODEV;
+	}
+
+	ret = devm_mfd_add_devices(dev, PLATFORM_DEVID_AUTO,
+				   ariel_ec_cells,
+				   ARRAY_SIZE(ariel_ec_cells),
+				   NULL, 0, NULL);
+	if (ret)
+		return ret;
+
+	if (of_property_read_bool(np, "system-power-controller")) {
+		ddata->off_gpios =
+			devm_gpiod_get_array_optional(dev, "off", GPIOD_IN);
+		if (IS_ERR(ddata->off_gpios))
+			return PTR_ERR(ddata->off_gpios);
+		if (ddata->off_gpios->ndescs < 2) {
+			dev_err(dev, "invalid off-gpios property\n");
+			return -EINVAL;
+		}
+	}
+
+	if (ddata->off_gpios) {
+		register_restart_handler(&kb3930_restart_nb);
+		if (!pm_power_off)
+			pm_power_off = kb3930_pm_power_off;
+	}
+
+	return 0;
+}
+
+static int kb3930_remove(struct i2c_client *client)
+{
+	struct kb3930 *ddata = i2c_get_clientdata(client);
+
+	if (ddata->off_gpios) {
+		if (pm_power_off == kb3930_pm_power_off)
+			pm_power_off = NULL;
+		unregister_restart_handler(&kb3930_restart_nb);
+	}
+	kb3930_power_off = NULL;
+
+	return 0;
+}
+
+static const struct of_device_id kb3930_dt_ids[] = {
+	{ .compatible = "ene,kb3930" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, kb3930_dt_ids);
+
+static struct i2c_driver kb3930_driver = {
+	.probe_new = kb3930_probe,
+	.remove = kb3930_remove,
+	.driver = {
+		.name = "ene-kb3930",
+		.of_match_table = of_match_ptr(kb3930_dt_ids),
+	},
+};
+module_i2c_driver(kb3930_driver);
+
+MODULE_AUTHOR("Lubomir Rintel <lkundrak@v3.sk>");
+MODULE_DESCRIPTION("ENE KB3930 Embedded Controller Driver");
+MODULE_LICENSE("Dual BSD/GPL");