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>

1 files changed, 13 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"