stm32h7/serial: Do not wait on TXDMA semaphore #11154
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If using flow control with a high CTS the thread may be blocked forever on the second transmit attempt due to waiting on the txdma semaphore. The calling thread can then never make progress and release any resources it has taken, thus may cause a deadlock in other parts of the system. The implementation differs in behavior from interrupt-driven TX and the STM32F7 TXDMA . It should not implicitly wait on a taken semaphore but return immediately and let the upper layers decide on what to do next.
davids5
approved these changes
Nov 8, 2023
pkarashchenko
approved these changes
Nov 8, 2023
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If using flow control with a high CTS the thread may be blocked forever on the second transmit attempt due to waiting on the txdma semaphore. The calling thread can then never make progress and release any resources it has taken, thus may cause a deadlock in other parts of the system.
The implementation differs in behavior from interrupt-driven TX and the STM32F7 TXDMA . It should not implicitly wait on a taken semaphore but return immediately and let the upper layers decide on what to do next.
See a more detailed analysis here: PX4/PX4-Autopilot#22302
cc @davids5