ec/google/chromeec: Add driver for i2c_tunnel device under Chrome EC

This change enables support for generating ACPI nodes for I2C tunnel for
any GOOG0012 device that is sitting behind the Chrome EC. It accepts a
config "remote_bus" which allows mainboard to configure the id of the
remote bus that is being tunneled.

BUG=b:154290952
BRANCH=None
TEST=Verified that SSDT node for I2C tunnel behind Chrome EC is
generated correctly.

Signed-off-by: Furquan Shaikh <furquan@google.com>
Change-Id: Icfc0ec3725d7f1d20bcb5cb43a0a23aac72bf4eb
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40515
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/ec/google/chromeec/Kconfig

@@ -196,3 +196,9 @@ config EC_GOOGLE_CHROMEEC_SWITCHES
 	help
 	  Enable support for Chrome OS mode switches provided by the Chrome OS
 	  EC.
+
+if EC_GOOGLE_CHROMEEC
+
+source "src/ec/google/chromeec/*/Kconfig"
+
+endif

src/ec/google/chromeec/Makefile.inc

@@ -1,5 +1,7 @@
 ifeq ($(CONFIG_EC_GOOGLE_CHROMEEC),y)
 
+subdirs-y += i2c_tunnel
+
 bootblock-$(CONFIG_EC_GOOGLE_CHROMEEC_BOARDID) += ec_boardid.c
 verstage-$(CONFIG_EC_GOOGLE_CHROMEEC_BOARDID) += ec_boardid.c
 romstage-$(CONFIG_EC_GOOGLE_CHROMEEC_BOARDID) += ec_boardid.c

src/ec/google/chromeec/i2c_tunnel/Kconfig

@@ -0,0 +1,6 @@
+config EC_GOOGLE_CHROMEEC_I2C_TUNNEL
+	bool
+	depends on HAVE_ACPI_TABLES
+	help
+	  This enables the Cros EC I2C tunnel driver that is required to fill the
+	  SSDT nodes for the I2C tunnel used by the mainboard.

src/ec/google/chromeec/i2c_tunnel/Makefile.inc

@@ -0,0 +1 @@
+ramstage-$(CONFIG_EC_GOOGLE_CHROMEEC_I2C_TUNNEL) += i2c_tunnel.c

src/ec/google/chromeec/i2c_tunnel/chip.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* This file is part of the coreboot project. */
+
+#ifndef __EC_GOOGLE_CHROMEEC_I2C_TUNNEL__
+#define __EC_GOOGLE_CHROMEEC_I2C_TUNNEL__
+
+struct ec_google_chromeec_i2c_tunnel_config {
+	/* ACPI device name */
+	const char *name;
+	/* ACPI _UID */
+	unsigned int uid;
+	/* EC I2C bus number we tunnel to on the other side. */
+	unsigned int remote_bus;
+};
+
+#endif /* __EC_GOOGLE_CHROMEEC_I2C_TUNNEL__ */

src/ec/google/chromeec/i2c_tunnel/i2c_tunnel.c

@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* This file is part of the coreboot project. */
+
+#include <arch/acpi_device.h>
+#include <arch/acpigen.h>
+#include <console/console.h>
+#include <device/device.h>
+#include <device/path.h>
+#include <string.h>
+#include "chip.h"
+
+#define CROS_EC_I2C_TUNNEL_HID		"GOOG0012"
+#define CROS_EC_I2C_TUNNEL_DDN		"Cros EC I2C Tunnel"
+
+static void crosec_i2c_tunnel_fill_ssdt(struct device *dev)
+{
+	const char *scope = acpi_device_scope(dev);
+	struct ec_google_chromeec_i2c_tunnel_config *cfg = dev->chip_info;
+	struct acpi_dp *dsd;
+
+	if (!dev->enabled || !scope || !cfg)
+		return;
+
+	acpigen_write_scope(scope);
+
+	acpigen_write_device(acpi_device_name(dev));
+	acpigen_write_name_string("_HID", CROS_EC_I2C_TUNNEL_HID);
+	acpigen_write_name_integer("_UID", cfg->uid);
+	acpigen_write_name_string("_DDN", CROS_EC_I2C_TUNNEL_DDN);
+	acpigen_write_STA(acpi_device_status(dev));
+
+	dsd = acpi_dp_new_table("_DSD");
+	acpi_dp_add_integer(dsd, "google,remote-bus", cfg->remote_bus);
+	acpi_dp_write(dsd);
+
+	acpigen_pop_len(); /* Device */
+	acpigen_pop_len(); /* Scope */
+
+	printk(BIOS_INFO, "%s: %s at %s\n", acpi_device_path(dev), CROS_EC_I2C_TUNNEL_DDN,
+						dev_path(dev));
+}
+
+static const char *crosec_i2c_tunnel_acpi_name(const struct device *dev)
+{
+	struct ec_google_chromeec_i2c_tunnel_config *cfg = dev->chip_info;
+	static char name[5];
+
+	if (cfg->name)
+		return cfg->name;
+
+	snprintf(name, sizeof(name), "TUN%X", dev->path.generic.id);
+	return name;
+}
+
+static struct device_operations crosec_i2c_tunnel_ops = {
+	.read_resources		= noop_read_resources,
+	.set_resources		= noop_set_resources,
+	.acpi_name		= crosec_i2c_tunnel_acpi_name,
+	.acpi_fill_ssdt		= crosec_i2c_tunnel_fill_ssdt,
+	.scan_bus		= scan_static_bus,
+};
+
+static void crosec_i2c_tunnel_enable(struct device *dev)
+{
+	dev->ops = &crosec_i2c_tunnel_ops;
+}
+
+struct chip_operations ec_google_chromeec_i2c_tunnel_ops = {
+	CHIP_NAME("CrosEC I2C Tunnel Device")
+	.enable_dev = crosec_i2c_tunnel_enable
+};