gpio: Add ChromeOS EC GPIO driver

The ChromeOS embedded controller (EC) supports setting the state of
GPIOs when the system is unlocked, and getting the state of GPIOs in all
cases. The GPIOs are on the EC itself, so the EC acts similar to a GPIO
expander. Add a driver to get and set the GPIOs on the EC through the
host command interface.

Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/gpio/Kconfig

@@ -1241,6 +1241,16 @@ config GPIO_BD9571MWV
 	  This driver can also be built as a module. If so, the module
 	  will be called gpio-bd9571mwv.
 
+config GPIO_CROS_EC
+	tristate "ChromeOS EC GPIO support"
+	depends on CROS_EC
+	help
+	  GPIO driver for the ChromeOS Embedded Controller (EC). GPIOs
+	  cannot be set unless the system is unlocked.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called gpio-cros-ec.
+
 config GPIO_CRYSTAL_COVE
 	tristate "GPIO support for Crystal Cove PMIC"
 	depends on (X86 || COMPILE_TEST) && INTEL_SOC_PMIC

drivers/gpio/Makefile

@@ -46,6 +46,7 @@ obj-$(CONFIG_GPIO_BT8XX)		+= gpio-bt8xx.o
 obj-$(CONFIG_GPIO_CADENCE)		+= gpio-cadence.o
 obj-$(CONFIG_GPIO_CLPS711X)		+= gpio-clps711x.o
 obj-$(CONFIG_GPIO_SNPS_CREG)		+= gpio-creg-snps.o
+obj-$(CONFIG_GPIO_CROS_EC)		+= gpio-cros-ec.o
 obj-$(CONFIG_GPIO_CRYSTAL_COVE)		+= gpio-crystalcove.o
 obj-$(CONFIG_GPIO_CS5535)		+= gpio-cs5535.o
 obj-$(CONFIG_GPIO_DA9052)		+= gpio-da9052.o

drivers/gpio/gpio-cros-ec.c

@@ -0,0 +1,209 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2024 Google LLC
+ *
+ * This driver provides the ability to control GPIOs on the Chrome OS EC.
+ * There isn't any direction control, and setting values on GPIOs is only
+ * possible when the system is unlocked.
+ */
+
+#include <linux/bitops.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/gpio/driver.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_data/cros_ec_commands.h>
+#include <linux/platform_data/cros_ec_proto.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+/* Prefix all names to avoid collisions with EC <-> AP nets */
+static const char cros_ec_gpio_prefix[] = "EC:";
+
+/* Setting gpios is only supported when the system is unlocked */
+static void cros_ec_gpio_set(struct gpio_chip *gc, unsigned int gpio, int val)
+{
+	const char *name = gc->names[gpio] + strlen(cros_ec_gpio_prefix);
+	struct cros_ec_device *cros_ec = gpiochip_get_data(gc);
+	struct ec_params_gpio_set params = {
+		.val = val,
+	};
+	int ret;
+	ssize_t copied;
+
+	copied = strscpy(params.name, name, sizeof(params.name));
+	if (copied < 0)
+		return;
+
+	ret = cros_ec_cmd(cros_ec, 0, EC_CMD_GPIO_SET, &params,
+			  sizeof(params), NULL, 0);
+	if (ret < 0)
+		dev_err(gc->parent, "error setting gpio%d (%s) on EC: %d\n", gpio, name, ret);
+}
+
+static int cros_ec_gpio_get(struct gpio_chip *gc, unsigned int gpio)
+{
+	const char *name = gc->names[gpio] + strlen(cros_ec_gpio_prefix);
+	struct cros_ec_device *cros_ec = gpiochip_get_data(gc);
+	struct ec_params_gpio_get params;
+	struct ec_response_gpio_get response;
+	int ret;
+	ssize_t copied;
+
+	copied = strscpy(params.name, name, sizeof(params.name));
+	if (copied < 0)
+		return -EINVAL;
+
+	ret = cros_ec_cmd(cros_ec, 0, EC_CMD_GPIO_GET, &params,
+			  sizeof(params), &response, sizeof(response));
+	if (ret < 0) {
+		dev_err(gc->parent, "error getting gpio%d (%s) on EC: %d\n", gpio, name, ret);
+		return ret;
+	}
+
+	return response.val;
+}
+
+#define CROS_EC_GPIO_INPUT         BIT(8)
+#define CROS_EC_GPIO_OUTPUT        BIT(9)
+
+static int cros_ec_gpio_get_direction(struct gpio_chip *gc, unsigned int gpio)
+{
+	const char *name = gc->names[gpio] + strlen(cros_ec_gpio_prefix);
+	struct cros_ec_device *cros_ec = gpiochip_get_data(gc);
+	struct ec_params_gpio_get_v1 params = {
+		.subcmd = EC_GPIO_GET_INFO,
+		.get_info.index = gpio,
+	};
+	struct ec_response_gpio_get_v1 response;
+	int ret;
+
+	ret = cros_ec_cmd(cros_ec, 1, EC_CMD_GPIO_GET, &params,
+			  sizeof(params), &response, sizeof(response));
+	if (ret < 0) {
+		dev_err(gc->parent, "error getting direction of gpio%d (%s) on EC: %d\n", gpio, name, ret);
+		return ret;
+	}
+
+	if (response.get_info.flags & CROS_EC_GPIO_INPUT)
+		return GPIO_LINE_DIRECTION_IN;
+
+	if (response.get_info.flags & CROS_EC_GPIO_OUTPUT)
+		return GPIO_LINE_DIRECTION_OUT;
+
+	return -EINVAL;
+}
+
+/* Query EC for all gpio line names */
+static int cros_ec_gpio_init_names(struct cros_ec_device *cros_ec, struct gpio_chip *gc)
+{
+	struct ec_params_gpio_get_v1 params = {
+		.subcmd = EC_GPIO_GET_INFO,
+	};
+	struct ec_response_gpio_get_v1 response;
+	int ret, i;
+	/* EC may not NUL terminate */
+	size_t name_len = strlen(cros_ec_gpio_prefix) + sizeof(response.get_info.name) + 1;
+	ssize_t copied;
+	const char **names;
+	char *str;
+
+	names = devm_kcalloc(gc->parent, gc->ngpio, sizeof(*names), GFP_KERNEL);
+	if (!names)
+		return -ENOMEM;
+	gc->names = names;
+
+	str = devm_kcalloc(gc->parent, gc->ngpio, name_len, GFP_KERNEL);
+	if (!str)
+		return -ENOMEM;
+
+	/* Get gpio line names one at a time */
+	for (i = 0; i < gc->ngpio; i++) {
+		params.get_info.index = i;
+		ret = cros_ec_cmd(cros_ec, 1, EC_CMD_GPIO_GET, &params,
+				  sizeof(params), &response, sizeof(response));
+		if (ret < 0) {
+			dev_err_probe(gc->parent, ret, "error getting gpio%d info\n", i);
+			return ret;
+		}
+
+		names[i] = str;
+		copied = scnprintf(str, name_len, "%s%s", cros_ec_gpio_prefix,
+				   response.get_info.name);
+		if (copied < 0)
+			return copied;
+
+		str += copied + 1;
+	}
+
+	return 0;
+}
+
+/* Query EC for number of gpios */
+static int cros_ec_gpio_ngpios(struct cros_ec_device *cros_ec)
+{
+	struct ec_params_gpio_get_v1 params = {
+		.subcmd = EC_GPIO_GET_COUNT,
+	};
+	struct ec_response_gpio_get_v1 response;
+	int ret;
+
+	ret = cros_ec_cmd(cros_ec, 1, EC_CMD_GPIO_GET, &params,
+			  sizeof(params), &response, sizeof(response));
+	if (ret < 0)
+		return ret;
+
+	return response.get_count.val;
+}
+
+static int cros_ec_gpio_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device *parent = dev->parent;
+	struct cros_ec_dev *ec_dev = dev_get_drvdata(parent);
+	struct cros_ec_device *cros_ec = ec_dev->ec_dev;
+	struct gpio_chip *gc;
+	int ngpios;
+	int ret;
+
+	/* Use the fwnode from the protocol device, e.g. cros-ec-spi */
+	device_set_node(dev, dev_fwnode(cros_ec->dev));
+
+	ngpios = cros_ec_gpio_ngpios(cros_ec);
+	if (ngpios < 0) {
+		dev_err_probe(dev, ngpios, "error getting gpio count\n");
+		return ngpios;
+	}
+
+	gc = devm_kzalloc(dev, sizeof(*gc), GFP_KERNEL);
+	if (!gc)
+		return -ENOMEM;
+
+	gc->ngpio = ngpios;
+	gc->parent = dev;
+	ret = cros_ec_gpio_init_names(cros_ec, gc);
+	if (ret)
+		return ret;
+
+	gc->can_sleep = true;
+	gc->label = dev_name(dev);
+	gc->base = -1;
+	gc->set = cros_ec_gpio_set;
+	gc->get = cros_ec_gpio_get;
+	gc->get_direction = cros_ec_gpio_get_direction;
+
+	return devm_gpiochip_add_data(dev, gc, cros_ec);
+}
+
+static struct platform_driver cros_ec_gpio_driver = {
+	.probe = cros_ec_gpio_probe,
+	.driver = {
+		.name = "cros-ec-gpio",
+	},
+};
+module_platform_driver(cros_ec_gpio_driver);
+
+MODULE_DESCRIPTION("ChromeOS EC GPIO Driver");
+MODULE_LICENSE("GPL");