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