platform/chrome: cros_typec_switch: Add switch driver

Introduce a driver to configure USB Type-C mode switches and retimers
which are controlled by the ChromeOS EC (Embedded Controller).
This allows Type-C port drivers, as well as alternate mode drivers to
configure their relevant mode switches and retimers according to the
Type-C state they want to achieve.

ACPI devices with ID GOOG001A will bind to this driver.

Currently, we only register a retimer switch with a stub set function.
Subsequent patches will implement the host command set functionality,
and introduce mode switches.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220816214857.2088914-3-pmalani@chromium.org

MAINTAINERS

@@ -4894,6 +4894,7 @@ M:	Prashant Malani <pmalani@chromium.org>
 L:	chrome-platform@lists.linux.dev
 S:	Maintained
 F:	drivers/platform/chrome/cros_ec_typec.c
+F:	drivers/platform/chrome/cros_typec_switch.c
 
 CHROMEOS EC USB PD NOTIFY DRIVER
 M:	Prashant Malani <pmalani@chromium.org>

drivers/platform/chrome/Kconfig

@@ -265,6 +265,17 @@ config CHROMEOS_PRIVACY_SCREEN
 	  this should probably always be built into the kernel to avoid or
 	  minimize drm probe deferral.
 
+config CROS_TYPEC_SWITCH
+	tristate "ChromeOS EC Type-C Switch Control"
+	depends on MFD_CROS_EC_DEV && TYPEC && ACPI
+	default MFD_CROS_EC_DEV
+	help
+	  If you say Y here, you get support for configuring the ChromeOS EC Type-C
+	  muxes and retimers.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called cros_typec_switch.
+
 source "drivers/platform/chrome/wilco_ec/Kconfig"
 
 # Kunit test cases

drivers/platform/chrome/Makefile

@@ -12,6 +12,7 @@ obj-$(CONFIG_CHROMEOS_TBMC)		+= chromeos_tbmc.o
 obj-$(CONFIG_CROS_EC)			+= cros_ec.o
 obj-$(CONFIG_CROS_EC_I2C)		+= cros_ec_i2c.o
 obj-$(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
 cros_ec_lpcs-objs			:= cros_ec_lpc.o cros_ec_lpc_mec.o

drivers/platform/chrome/cros_typec_switch.c

@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2022 Google LLC
+ *
+ * This driver provides the ability to configure Type-C muxes and retimers which are controlled by
+ * the ChromeOS EC.
+ */
+
+#include <linux/acpi.h>
+#include <linux/module.h>
+#include <linux/platform_data/cros_ec_commands.h>
+#include <linux/platform_device.h>
+#include <linux/usb/typec_retimer.h>
+
+#define DRV_NAME "cros-typec-switch"
+
+/* Handles and other relevant data required for each port's switches. */
+struct cros_typec_port {
+	int port_num;
+	struct typec_retimer *retimer;
+	struct cros_typec_switch_data *sdata;
+};
+
+/* Driver-specific data. */
+struct cros_typec_switch_data {
+	struct device *dev;
+	struct cros_ec_device *ec;
+	struct cros_typec_port *ports[EC_USB_PD_MAX_PORTS];
+};
+
+static int cros_typec_retimer_set(struct typec_retimer *retimer, struct typec_retimer_state *state)
+{
+	return 0;
+}
+
+static void cros_typec_unregister_switches(struct cros_typec_switch_data *sdata)
+{
+	int i;
+
+	for (i = 0; i < EC_USB_PD_MAX_PORTS; i++) {
+		if (!sdata->ports[i])
+			continue;
+		typec_retimer_unregister(sdata->ports[i]->retimer);
+	}
+}
+
+static int cros_typec_register_retimer(struct cros_typec_port *port, struct fwnode_handle *fwnode)
+{
+	struct typec_retimer_desc retimer_desc = {
+		.fwnode = fwnode,
+		.drvdata = port,
+		.name = fwnode_get_name(fwnode),
+		.set = cros_typec_retimer_set,
+	};
+
+	port->retimer = typec_retimer_register(port->sdata->dev, &retimer_desc);
+	if (IS_ERR(port->retimer))
+		return PTR_ERR(port->retimer);
+
+	return 0;
+}
+
+static int cros_typec_register_switches(struct cros_typec_switch_data *sdata)
+{
+	struct cros_typec_port *port;
+	struct device *dev = sdata->dev;
+	struct fwnode_handle *fwnode;
+	struct acpi_device *adev;
+	unsigned long long index;
+	int nports, ret;
+
+	nports = device_get_child_node_count(dev);
+	if (nports == 0) {
+		dev_err(dev, "No switch devices found.\n");
+		return -ENODEV;
+	}
+
+	device_for_each_child_node(dev, fwnode) {
+		port = devm_kzalloc(dev, sizeof(*port), GFP_KERNEL);
+		if (!port) {
+			ret = -ENOMEM;
+			goto err_switch;
+		}
+
+		adev = to_acpi_device_node(fwnode);
+		if (!adev) {
+			dev_err(fwnode->dev, "Couldn't get ACPI device handle\n");
+			ret = -ENODEV;
+			goto err_switch;
+		}
+
+		ret = acpi_evaluate_integer(adev->handle, "_ADR", NULL, &index);
+		if (ACPI_FAILURE(ret)) {
+			dev_err(fwnode->dev, "_ADR wasn't evaluated\n");
+			ret = -ENODATA;
+			goto err_switch;
+		}
+
+		if (index < 0 || index >= EC_USB_PD_MAX_PORTS) {
+			dev_err(fwnode->dev, "Invalid port index number: %llu", index);
+			ret = -EINVAL;
+			goto err_switch;
+		}
+		port->sdata = sdata;
+		port->port_num = index;
+		sdata->ports[index] = port;
+
+		ret = cros_typec_register_retimer(port, fwnode);
+		if (ret) {
+			dev_err(dev, "Retimer switch register failed\n");
+			goto err_switch;
+		}
+
+		dev_dbg(dev, "Retimer switch registered for index %llu\n", index);
+	}
+
+	return 0;
+err_switch:
+	cros_typec_unregister_switches(sdata);
+	return ret;
+}
+
+static int cros_typec_switch_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct cros_typec_switch_data *sdata;
+
+	sdata = devm_kzalloc(dev, sizeof(*sdata), GFP_KERNEL);
+	if (!sdata)
+		return -ENOMEM;
+
+	sdata->dev = dev;
+	sdata->ec = dev_get_drvdata(pdev->dev.parent);
+
+	platform_set_drvdata(pdev, sdata);
+
+	return cros_typec_register_switches(sdata);
+}
+
+static int cros_typec_switch_remove(struct platform_device *pdev)
+{
+	struct cros_typec_switch_data *sdata = platform_get_drvdata(pdev);
+
+	cros_typec_unregister_switches(sdata);
+	return 0;
+}
+
+#ifdef CONFIG_ACPI
+static const struct acpi_device_id cros_typec_switch_acpi_id[] = {
+	{ "GOOG001A", 0 },
+	{}
+};
+MODULE_DEVICE_TABLE(acpi, cros_typec_switch_acpi_id);
+#endif
+
+static struct platform_driver cros_typec_switch_driver = {
+	.driver	= {
+		.name = DRV_NAME,
+		.acpi_match_table = ACPI_PTR(cros_typec_switch_acpi_id),
+	},
+	.probe = cros_typec_switch_probe,
+	.remove = cros_typec_switch_remove,
+};
+
+module_platform_driver(cros_typec_switch_driver);
+
+MODULE_AUTHOR("Prashant Malani <pmalani@chromium.org>");
+MODULE_DESCRIPTION("ChromeOS EC Type-C Switch control");
+MODULE_LICENSE("GPL");