I2C: Add reg-shift = <2>; to device tree #174
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Commit 72e4b60 made the I2C control registers 32-bit aligned to match the rest of the system. However, the OpenCores I2C driver (https://github.com/torvalds/linux/blob/master/drivers/i2c/busses/i2c-ocores.c) expects registers to be 8-bit aligned. In cases where a user relies on a generated device tree instead of a custom one (e.g. in HiFive bootloaders https://github.com/sifive/freedom-u540-c000-bootloader/blob/master/fsbl/ux00_fsbl.dts#L300), the I2C block will not be functional because control registers will be improperly written. Setting `reg-shift = <2>;` this way allows the OpenCores driver to work properly by default. This may break some custom drivers out there, but in the case of the Zephyr project driver (https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/i2c/i2c_sifive.c), this property is unused because it already expects 32-bit aligned registers.
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Commit 72e4b60 made the I2C control registers 32-bit aligned to match the rest of the system. However, the OpenCores I2C driver (https://github.com/torvalds/linux/blob/master/drivers/i2c/busses/i2c-ocores.c) expects registers to be 8-bit aligned.
In cases where a user relies on a generated device tree instead of a custom one (e.g. in HiFive bootloaders https://github.com/sifive/freedom-u540-c000-bootloader/blob/master/fsbl/ux00_fsbl.dts#L300), the I2C block will not be functional because control registers will be improperly written. Setting
reg-shift = <2>;this way allows the OpenCores driver to work properly by default.This may break some custom drivers out there, but in the case of the Zephyr project driver (https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/i2c/i2c_sifive.c), this property is unused because it already expects 32-bit aligned registers.
Potentially addresses #154. Special thanks to @a0u for debugging.