u-boot/doc/device-tree-bindings/i2c/i2c.txt
Lukasz Majewski a40fe217d1 DM: I2C: Introduce 'u-boot, i2c-transaction-bytes' property
The 'u-boot,i2c-transaction-bytes' device tree property provides
information regarding number of bytes transferred by a device in a
single transaction.

This change is necessary to avoid hanging devices after soft reset.
One notable example is communication with MC34708 device:

1. Reset when communicating with MC34708 via I2C.

2. The u-boot (after reboot -f) tries to setup the I2C and then calls
force_idle_bus. In the same time MC34708 still has some data to be sent
(as it transfers data in 24 bits chunks).

3. The force_idle_bus() is not able to make the bus idle as 8 SCL
clocks may be not enough to have the full transmission.

4. We end up with I2C inconsistency with MC34708.

This PMIC device requires 24+ SCL cycles to make finish any pending I2C
transmission.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
2019-04-11 15:21:33 +02:00

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U-Boot I2C
----------
U-Boot's I2C model has the concept of an offset within a chip (I2C target
device). The offset can be up to 4 bytes long, but is normally 1 byte,
meaning that offsets from 0 to 255 are supported by the chip. This often
corresponds to register numbers.
Apart from the controller-specific I2C bindings, U-Boot supports a special
property which allows the chip offset length to be selected.
Optional properties:
- u-boot,i2c-offset-len - length of chip offset in bytes. If omitted the
default value of 1 is used.
- u-boot,i2c-transaction-bytes - the length of single I2C transaction on
the bus. Some devices require more than single byte transmission
(e.g. mc34708 mfd). This information is necessary to correctly
initialize (put into idle state) I2C bus after soft reset.
- gpios = <sda ...>, <scl ...>;
pinctrl-names = "default", "gpio";
pinctrl-0 = <&i2c_xfer>;
pinctrl-1 = <&i2c_gpio>;
Pin description for I2C bus software deblocking.
Example
-------
i2c4: i2c@12ca0000 {
cros-ec@1e {
reg = <0x1e>;
compatible = "google,cros-ec";
i2c-max-frequency = <100000>;
u-boot,i2c-offset-len = <0>;
u-boot,i2c-transaction-bytes = <3>;
ec-interrupt = <&gpx1 6 GPIO_ACTIVE_LOW>;
};
};
&i2c1 {
pinctrl-names = "default", "gpio";
pinctrl-0 = <&i2c1_xfer>;
pinctrl-1 = <&i2c1_gpio>;
gpios = <&gpio1 26 GPIO_ACTIVE_LOW>, /* SDA */
<&gpio1 27 GPIO_ACTIVE_LOW>; /* SCL */
};