mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-11-07 21:54:45 +00:00
a40fe217d1
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>
46 lines
1.4 KiB
Text
46 lines
1.4 KiB
Text
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 */
|
|
};
|