[v10,1/3] platform/chrome: cros_ec_uart: Add cros-ec-uart transport layer

diff --git a/MAINTAINERS b/MAINTAINERS
index 4002d61291ca7..1b54bd6f28328 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4913,6 +4913,13 @@  S:	Maintained
 F:	Documentation/devicetree/bindings/sound/google,cros-ec-codec.yaml
 F:	sound/soc/codecs/cros_ec_codec.*
 
+CHROMEOS EC UART DRIVER
+M:	Bhanu Prakash Maiya <bhanumaiya@chromium.org>
+R:	Benson Leung <bleung@chromium.org>
+R:	Tzung-Bi Shih <tzungbi@kernel.org>
+S:	Maintained
+F:	drivers/platform/chrome/cros_ec_uart.c
+
 CHROMEOS EC SUBDRIVERS
 M:	Benson Leung <bleung@chromium.org>
 R:	Guenter Roeck <groeck@chromium.org>
diff --git a/drivers/platform/chrome/Kconfig b/drivers/platform/chrome/Kconfig
index c1ca247987d2d..0d272c87f32b2 100644
--- a/drivers/platform/chrome/Kconfig
+++ b/drivers/platform/chrome/Kconfig
@@ -119,6 +119,16 @@  config CROS_EC_SPI
 	  response time cannot be guaranteed, we support ignoring
 	  'pre-amble' bytes before the response actually starts.
 
+config CROS_EC_UART
+	tristate "ChromeOS Embedded Controller (UART)"
+	depends on CROS_EC && ACPI && SERIAL_DEV_BUS
+	help
+	  If you say Y here, you get support for talking to the ChromeOS EC
+	  through a UART, using a byte-level protocol.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called cros_ec_uart.
+
 config CROS_EC_LPC
 	tristate "ChromeOS Embedded Controller (LPC)"
 	depends on CROS_EC && ACPI && (X86 || COMPILE_TEST)
diff --git a/drivers/platform/chrome/Makefile b/drivers/platform/chrome/Makefile
index f6068d077a40a..0f39edef660dd 100644
--- a/drivers/platform/chrome/Makefile
+++ b/drivers/platform/chrome/Makefile
@@ -15,6 +15,7 @@  obj-$(CONFIG_CROS_EC_ISHTP)		+= cros_ec_ishtp.o
 obj-$(CONFIG_CROS_TYPEC_SWITCH)		+= cros_typec_switch.o
 obj-$(CONFIG_CROS_EC_RPMSG)		+= cros_ec_rpmsg.o
 obj-$(CONFIG_CROS_EC_SPI)		+= cros_ec_spi.o
+obj-$(CONFIG_CROS_EC_UART)		+= cros_ec_uart.o
 cros_ec_lpcs-objs			:= cros_ec_lpc.o cros_ec_lpc_mec.o
 obj-$(CONFIG_CROS_EC_TYPEC)		+= cros_ec_typec.o
 obj-$(CONFIG_CROS_EC_LPC)		+= cros_ec_lpcs.o
diff --git a/drivers/platform/chrome/cros_ec_uart.c b/drivers/platform/chrome/cros_ec_uart.c
new file mode 100644
index 0000000000000..873aee4172bfd
--- /dev/null
+++ b/drivers/platform/chrome/cros_ec_uart.c
@@ -0,0 +1,357 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * UART interface for ChromeOS Embedded Controller
+ *
+ * Copyright 2020-2022 Google LLC.
+ */
+
+#include <linux/acpi.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_data/cros_ec_proto.h>
+#include <linux/serdev.h>
+#include <linux/slab.h>
+#include <uapi/linux/sched/types.h>
+
+#include "cros_ec.h"
+
+/*
+ * EC sends contiguous bytes of response packet on UART AP RX.
+ * TTY driver in AP accumulates incoming bytes and calls the registered callback
+ * function. Byte count can range from 1 to MAX bytes supported by EC.
+ * This driver should wait for long time for all callbacks to be processed.
+ * Considering the worst case scenario, wait for 500 msec. This timeout should
+ * account for max latency and some additional guard time.
+ * Best case: Entire packet is received in ~200 ms, wait queue will be released
+ * and packet will be processed.
+ * Worst case: TTY driver sends bytes in multiple callbacks. In this case this
+ * driver will wait for ~1 sec beyond which it will timeout.
+ * This timeout value should not exceed ~500 msec because in case if
+ * EC_CMD_REBOOT_EC sent, high level driver should be able to intercept EC
+ * in RO.
+ */
+#define EC_MSG_DEADLINE_MS		500
+
+/**
+ * struct response_info - Encapsulate EC response related
+ *			information for passing between function
+ *			cros_ec_uart_pkt_xfer() and cros_ec_uart_rx_bytes()
+ *			callback.
+ * @data:		Copy the data received from EC here.
+ * @max_size:		Max size allocated for the @data buffer. If the
+ *			received data exceeds this value, we log an error.
+ * @size:		Actual size of data received from EC. This is also
+ *			used to accumulate byte count with response is received
+ *			in dma chunks.
+ * @exp_len:		Expected bytes of response from EC including header.
+ * @status:		Re-init to 0 before sending a cmd. Updated to 1 when
+ *			a response is successfully received, or a negative
+ *			integer on failure.
+ * @wait_queue:	Wait queue EC response where the cros_ec sends request
+ *			to EC and waits
+ */
+struct response_info {
+	void *data;
+	size_t max_size;
+	size_t size;
+	size_t exp_len;
+	int status;
+	wait_queue_head_t wait_queue;
+};
+
+/**
+ * struct cros_ec_uart - information about a uart-connected EC
+ *
+ * @serdev_device:	serdev uart device we are connected to.
+ * @baudrate:		UART baudrate of attached EC device.
+ * @flowcontrol:	UART flowcontrol of attached device.
+ * @irq:		Linux IRQ number of associated serial device.
+ * @response:		Response info passing between cros_ec_uart_pkt_xfer()
+ *			and cros_ec_uart_rx_bytes()
+ */
+struct cros_ec_uart {
+	struct serdev_device *serdev;
+	u32 baudrate;
+	u8 flowcontrol;
+	u32 irq;
+	struct response_info response;
+};
+
+static int cros_ec_uart_rx_bytes(struct serdev_device *serdev,
+				 const u8 *data,
+				 size_t count)
+{
+	struct ec_host_response *response;
+	struct cros_ec_device *ec_dev = serdev_device_get_drvdata(serdev);
+	struct cros_ec_uart *ec_uart = ec_dev->priv;
+
+	/* Check if bytes were sent out of band */
+	if (!ec_uart->response.data) {
+		/* Discard all bytes */
+		dev_warn(ec_dev->dev, "Bytes received out of band, dropping them.\n");
+		return count;
+	}
+
+	/*
+	 * Check if incoming bytes + response.size is greater than allocated
+	 * buffer in din by cros_ec. This will ensure that if EC sends more
+	 * bytes than max_size, waiting process will be notified with an error.
+	 */
+	if (ec_uart->response.size + count > ec_uart->response.max_size) {
+		ec_uart->response.status = -EMSGSIZE;
+		wake_up(&ec_uart->response.wait_queue);
+		return count;
+	}
+
+	memcpy(ec_uart->response.data + ec_uart->response.size, data, count);
+
+	ec_uart->response.size += count;
+
+	/*
+	 * Read data_len if we received response header and if exp_len
+	 * was not read before.
+	 */
+	if (ec_uart->response.size >= sizeof(*response) &&
+	    ec_uart->response.exp_len == 0) {
+		response = (struct ec_host_response *) ec_uart->response.data;
+		ec_uart->response.exp_len = response->data_len + sizeof(*response);
+	}
+
+	/*
+	 * If driver received response header and payload from EC,
+	 * Wake up the wait queue.
+	 */
+	if (ec_uart->response.size >= sizeof(*response) &&
+	    ec_uart->response.size == ec_uart->response.exp_len) {
+		ec_uart->response.status = 1;
+		wake_up(&ec_uart->response.wait_queue);
+	}
+
+	return count;
+}
+
+static int cros_ec_uart_pkt_xfer(struct cros_ec_device *ec_dev,
+				 struct cros_ec_command *ec_msg)
+{
+	struct cros_ec_uart *ec_uart = ec_dev->priv;
+	struct serdev_device *serdev = ec_uart->serdev;
+	struct ec_host_response *response;
+	unsigned int len;
+	int ret, i;
+	u8 sum = 0;
+
+	len = cros_ec_prepare_tx(ec_dev, ec_msg);
+	dev_dbg(ec_dev->dev, "Prepared len=%d\n", len);
+
+	/* Setup for incoming response */
+	ec_uart->response.data = ec_dev->din;
+	ec_uart->response.max_size = ec_dev->din_size;
+	ec_uart->response.size = 0;
+	ec_uart->response.exp_len = 0;
+	ec_uart->response.status = 0;
+
+	ret = serdev_device_write_buf(serdev, ec_dev->dout, len);
+	if (ret < len) {
+		dev_err(ec_dev->dev, "Unable to write data");
+		ret = -EIO;
+		goto exit;
+	}
+
+	ret = wait_event_timeout(ec_uart->response.wait_queue,
+				 ec_uart->response.status,
+				 msecs_to_jiffies(EC_MSG_DEADLINE_MS));
+	if (ret == 0) {
+		dev_warn(ec_dev->dev, "Timed out waiting for response.\n");
+		ret = -ETIMEDOUT;
+		goto exit;
+	}
+
+	if (ec_uart->response.status < 0) {
+		dev_warn(ec_dev->dev, "Error response received: %d\n", ec_uart->response.status);
+		ret = ec_uart->response.status;
+		goto exit;
+	}
+
+	response = (struct ec_host_response *)ec_dev->din;
+	ec_msg->result = response->result;
+
+	if (response->data_len > ec_msg->insize) {
+		dev_err(ec_dev->dev, "Resp too long (%d bytes, expected %d)", response->data_len,
+			ec_msg->insize);
+		ret = -ENOSPC;
+		goto exit;
+	}
+
+	/* Validate checksum */
+	for (i = 0; i < sizeof(*response) + response->data_len; i++)
+		sum += ec_dev->din[i];
+
+	if (sum) {
+		dev_err(ec_dev->dev, "Bad packet checksum calculated %x\n", sum);
+		ret = -EBADMSG;
+		goto exit;
+	}
+
+	memcpy(ec_msg->data, ec_dev->din + sizeof(*response), response->data_len);
+
+	ret = response->data_len;
+
+exit:
+	/* Invalidate response buffer to guard against out of band rx data */
+	ec_uart->response.data = NULL;
+
+	if (ec_msg->command == EC_CMD_REBOOT_EC)
+		msleep(EC_REBOOT_DELAY_MS);
+
+	return ret;
+}
+
+static int cros_ec_uart_resource(struct acpi_resource *ares, void *data)
+{
+	struct cros_ec_uart *ec_uart = data;
+	struct acpi_resource_uart_serialbus *sb = &ares->data.uart_serial_bus;
+
+	if (ares->type == ACPI_RESOURCE_TYPE_SERIAL_BUS &&
+	    sb->type == ACPI_RESOURCE_SERIAL_TYPE_UART) {
+		ec_uart->baudrate = sb->default_baud_rate;
+		dev_dbg(&ec_uart->serdev->dev, "Baudrate %d\n", ec_uart->baudrate);
+
+		ec_uart->flowcontrol = sb->flow_control;
+		dev_dbg(&ec_uart->serdev->dev, "Flow control %d\n", ec_uart->flowcontrol);
+	}
+
+	return 0;
+}
+
+static int cros_ec_uart_acpi_probe(struct cros_ec_uart *ec_uart)
+{
+	int ret;
+	LIST_HEAD(resources);
+	struct acpi_device *adev = ACPI_COMPANION(&ec_uart->serdev->dev);
+
+	ret = acpi_dev_get_resources(adev, &resources, cros_ec_uart_resource, ec_uart);
+	if (ret < 0)
+		return ret;
+
+	acpi_dev_free_resource_list(&resources);
+
+	/* Retrieve GpioInt and translate it to Linux IRQ number */
+	ret = acpi_dev_gpio_irq_get(adev, 0);
+	if (ret < 0)
+		return ret;
+
+	ec_uart->irq = ret;
+	dev_dbg(&ec_uart->serdev->dev, "IRQ number %d\n", ec_uart->irq);
+
+	return 0;
+}
+
+static const struct serdev_device_ops cros_ec_uart_client_ops = {
+	.receive_buf = cros_ec_uart_rx_bytes,
+};
+
+static int cros_ec_uart_probe(struct serdev_device *serdev)
+{
+	struct device *dev = &serdev->dev;
+	struct cros_ec_device *ec_dev;
+	struct cros_ec_uart *ec_uart;
+	int ret;
+
+	ec_uart = devm_kzalloc(dev, sizeof(*ec_uart), GFP_KERNEL);
+	if (!ec_uart)
+		return -ENOMEM;
+
+	ec_dev = devm_kzalloc(dev, sizeof(*ec_dev), GFP_KERNEL);
+	if (!ec_dev)
+		return -ENOMEM;
+
+	ec_uart->serdev = serdev;
+
+	ret = devm_serdev_device_open(dev, ec_uart->serdev);
+	if (ret) {
+		dev_err(dev, "Unable to open UART device");
+		return ret;
+	}
+
+	serdev_device_set_drvdata(serdev, ec_dev);
+	serdev_device_set_client_ops(serdev, &cros_ec_uart_client_ops);
+	init_waitqueue_head(&ec_uart->response.wait_queue);
+
+	ret = cros_ec_uart_acpi_probe(ec_uart);
+	if (ret < 0) {
+		dev_err(dev, "Failed to get ACPI info (%d)", ret);
+		return ret;
+	}
+
+	ret = serdev_device_set_baudrate(serdev, ec_uart->baudrate);
+	if (ret < 0) {
+		dev_err(dev, "Failed to set up host baud rate (%d)", ret);
+		return ret;
+	}
+
+	serdev_device_set_flow_control(serdev, ec_uart->flowcontrol);
+
+	/* Initialize ec_dev for cros_ec  */
+	ec_dev->phys_name = dev_name(dev);
+	ec_dev->dev = dev;
+	ec_dev->priv = ec_uart;
+	ec_dev->irq = ec_uart->irq;
+	ec_dev->cmd_xfer = NULL;
+	ec_dev->pkt_xfer = cros_ec_uart_pkt_xfer;
+	ec_dev->din_size = sizeof(struct ec_host_response) +
+			   sizeof(struct ec_response_get_protocol_info);
+	ec_dev->dout_size = sizeof(struct ec_host_request);
+
+	return cros_ec_register(ec_dev);
+}
+
+static void cros_ec_uart_remove(struct serdev_device *serdev)
+{
+	struct cros_ec_device *ec_dev = serdev_device_get_drvdata(serdev);
+
+	cros_ec_unregister(ec_dev);
+};
+
+static int __maybe_unused cros_ec_uart_suspend(struct device *dev)
+{
+	struct cros_ec_device *ec_dev = dev_get_drvdata(dev);
+
+	return cros_ec_suspend(ec_dev);
+}
+
+static int __maybe_unused cros_ec_uart_resume(struct device *dev)
+{
+	struct cros_ec_device *ec_dev = dev_get_drvdata(dev);
+
+	return cros_ec_resume(ec_dev);
+}
+
+static SIMPLE_DEV_PM_OPS(cros_ec_uart_pm_ops, cros_ec_uart_suspend,
+			 cros_ec_uart_resume);
+
+#ifdef CONFIG_ACPI
+static const struct acpi_device_id cros_ec_uart_acpi_id[] = {
+	{ "GOOG0019", 0 }
+};
+
+MODULE_DEVICE_TABLE(acpi, cros_ec_uart_acpi_id);
+#endif
+
+static struct serdev_device_driver cros_ec_uart_driver = {
+	.driver	= {
+		.name	= "cros-ec-uart",
+		.acpi_match_table = ACPI_PTR(cros_ec_uart_acpi_id),
+		.pm	= &cros_ec_uart_pm_ops,
+	},
+	.probe		= cros_ec_uart_probe,
+	.remove		= cros_ec_uart_remove,
+};
+
+module_serdev_device_driver(cros_ec_uart_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("UART interface for ChromeOS Embedded Controller");
+MODULE_AUTHOR("Bhanu Prakash Maiya <bhanumaiya@chromium.org>");