cros_ec: Support the LDO access method used by spring

Add a driver to support the special LDO access used by spring. This is a
custom method in the cros_ec protocol - it does not use an I2C
pass-through.

There are two implementation choices:

1. Write a special LDO driver which can talk across the EC. Duplicate all
the logic from TPS65090 for retrying when the LDO fails to come up.

2. Write a special I2C bus driver which pretends to be a TPS65090 and
transfers reads and writes using the LDO message.

Either is distasteful. The latter method is chosen since it results in less
code duplication and a fairly simple (30-line) implementation of the core
logic.

The crosec 'ldo' subcommand could be removed (since i2c md/mw will work
instead) but is retained as a convenience.

Signed-off-by: Simon Glass <sjg@chromium.org>

3 files changed, 91 insertions, 0 deletions

diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
index e861b53..9a62ddd 100644
--- a/drivers/i2c/Kconfig
+++ b/drivers/i2c/Kconfig
@@ -29,6 +29,19 @@ config I2C_CROS_EC_TUNNEL
 	  I2C or LPC). Some Chromebooks use this when the hardware design
 	  does not allow direct access to the main PMIC from the AP.
 
+config I2C_CROS_EC_LDO
+	bool "Provide access to LDOs on the Chrome OS EC"
+	depends on CROS_EC
+	---help---
+	On many Chromebooks the main PMIC is inaccessible to the AP. This is
+	often dealt with by using an I2C pass-through interface provided by
+	the EC. On some unfortunate models (e.g. Spring) the pass-through
+	is not available, and an LDO message is available instead. This
+	option enables a driver which provides very basic access to those
+	regulators, via the EC. We implement this as an I2C bus	which
+	emulates just the TPS65090 messages we know about. This is done to
+	avoid duplicating the logic in the TPS65090 regulator driver for
+	enabling/disabling an LDO.
 
 config DM_I2C_GPIO
 	bool "Enable Driver Model for software emulated I2C bus driver"
diff --git a/drivers/i2c/Makefile b/drivers/i2c/Makefile
index 7f01fce..9b45248 100644
--- a/drivers/i2c/Makefile
+++ b/drivers/i2c/Makefile
@@ -8,6 +8,7 @@ obj-$(CONFIG_DM_I2C) += i2c-uclass.o
 obj-$(CONFIG_DM_I2C_COMPAT) += i2c-uclass-compat.o
 obj-$(CONFIG_DM_I2C_GPIO) += i2c-gpio.o
 obj-$(CONFIG_I2C_CROS_EC_TUNNEL) += cros_ec_tunnel.o
+obj-$(CONFIG_I2C_CROS_EC_LDO) += cros_ec_ldo.o
 
 obj-$(CONFIG_SYS_I2C_ADI) += adi_i2c.o
 obj-$(CONFIG_I2C_MV) += mv_i2c.o
diff --git a/drivers/i2c/cros_ec_ldo.c b/drivers/i2c/cros_ec_ldo.c
new file mode 100644
index 0000000..b817c61
--- /dev/null
+++ b/drivers/i2c/cros_ec_ldo.c
@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <cros_ec.h>
+#include <errno.h>
+#include <i2c.h>
+#include <power/tps65090.h>
+
+static int cros_ec_ldo_set_bus_speed(struct udevice *dev, unsigned int speed)
+{
+	return 0;
+}
+
+static int cros_ec_ldo_xfer(struct udevice *dev, struct i2c_msg *msg,
+			    int nmsgs)
+{
+	bool is_read = nmsgs > 1;
+	int fet_id, ret;
+
+	/*
+	 * Look for reads and writes of the LDO registers. In either case the
+	 * first message is a write with the register number as the first byte.
+	 */
+	if (!nmsgs || !msg->len || (msg->flags & I2C_M_RD)) {
+		debug("%s: Invalid message\n", __func__);
+		goto err;
+	}
+
+	fet_id = msg->buf[0] - REG_FET_BASE;
+	if (fet_id < 1 || fet_id > MAX_FET_NUM) {
+		debug("%s: Invalid FET %d\n", __func__, fet_id);
+		goto err;
+	}
+
+	if (is_read) {
+		uint8_t state;
+
+		ret = cros_ec_get_ldo(dev->parent, fet_id, &state);
+		if (!ret)
+			msg[1].buf[0] = state ?
+				FET_CTRL_ENFET | FET_CTRL_PGFET : 0;
+	} else {
+		bool on = msg->buf[1] & FET_CTRL_ENFET;
+
+		ret = cros_ec_set_ldo(dev->parent, fet_id, on);
+	}
+
+	return ret;
+
+err:
+	/* Indicate that the message is unimplemented */
+	return -ENOSYS;
+}
+
+static const struct dm_i2c_ops cros_ec_i2c_ops = {
+	.xfer		= cros_ec_ldo_xfer,
+	.set_bus_speed	= cros_ec_ldo_set_bus_speed,
+};
+
+static const struct udevice_id cros_ec_i2c_ids[] = {
+	{ .compatible = "google,cros-ec-ldo-tunnel" },
+	{ }
+};
+
+U_BOOT_DRIVER(cros_ec_ldo) = {
+	.name	= "cros_ec_ldo_tunnel",
+	.id	= UCLASS_I2C,
+	.of_match = cros_ec_i2c_ids,
+	.per_child_auto_alloc_size = sizeof(struct dm_i2c_chip),
+	.ops	= &cros_ec_i2c_ops,
+};