From f7da577027c81399d363332c150cd26d37356a6e Mon Sep 17 00:00:00 2001 From: Niklas Hauser Date: Wed, 8 Nov 2023 14:52:59 +0100 Subject: [PATCH] stm32h7/serial: Do not wait on TXDMA semaphore 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. --- arch/arm/src/stm32h7/stm32_serial.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/arch/arm/src/stm32h7/stm32_serial.c b/arch/arm/src/stm32h7/stm32_serial.c index 4b8048ed58b83..75971f1a1180f 100644 --- a/arch/arm/src/stm32h7/stm32_serial.c +++ b/arch/arm/src/stm32h7/stm32_serial.c @@ -3369,9 +3369,11 @@ static void up_dma_txavailable(struct uart_dev_s *dev) /* Only send when the DMA is idle */ - nxsem_wait(&priv->txdmasem); - - uart_xmitchars_dma(dev); + int rv = nxsem_trywait(&priv->txdmasem); + if (rv == OK) + { + uart_xmitchars_dma(dev); + } } #endif