Review of concept of changing UART flow control from Kconfig to DTS config


lairdjm
 

Hi,

I only noticed today that the Kconfig option for enabling hardware flow control on UARTs, which used to be an optional Kconfig option, was removed and replaced with a DTS boards file configuration option instead, as per https://github.com/zephyrproject-rtos/zephyr/pull/25999

I find this to be a bit of a step backwards for application development, we have many boards in zephyr that we and customers use, these boards might be used for something simple like a sensor or might be used alongside a PC for doing some heavy processing and message passing over Bluetooth, so with a sensor, the log system might be active but it won’t have anything connected to it most of the time unless there’s an issue, so flow control is not required here, if it’s enabled then it’s going to cause an issue once the UART buffer gets full. However, on a PC communications module, that would be using the UART constantly, and need data integrity so needs flow control – in the old system, the boards file would have the flow control pins and it would be disabled by default, a project could enable it with a Kconfig option, this was great. However with the new system, it seems that we need to force flow control on all our boards, and then in instances where it’s not needed, have an overlay for that specific board (and we have many boards) to delete the hardware flow control part. This means that to enable hardware flow control, we need to update our boards file then add an overlay to almost every sample application in zephyr for most of our boards to disable flow control. This seems a bit chaotic to me so I would like to revisit this concept of having flow control configurable as a Kconfig option, the pins should be defined in the DTS file which hasn’t changed but if flow control is needed or not should be controlled on a project basis, opt in not opt out.

 

Are there any thoughts on this subject and how to get this working, focused on ease of being able to set this for ours and customer’s reuse?

Thanks,

Jamie

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