When using the serial port as RS485 port, the tx statemachine is used to control the RTS pin to drive the RS485 transceiver TX_EN pin. When the TTY port is closed in the middle of a transmission (for instance during userland application crash), imx_uart_shutdown disables the interface and disables the Transmission Complete interrupt. afer that, imx_uart_stop_tx bails on an incomplete transmission, to be retriggered by the TC interrupt. This interrupt is disabled and therefore the tx statemachine never transitions out of SEND. The statemachine is in deadlock now, and the TX_EN remains low, making the interface useless. imx_uart_stop_tx now checks for incomplete transmission AND whether TC interrupts are enabled before bailing to be retriggered. This makes sure the state machine handling is reached, and is properly set to WAIT_AFTER_SEND.
Created kernel tracking bugs for this issue: Affects: fedora-all [bug 2265804]
Issue introduced in 5.9 with commit cb1a60923609 and fixed in 5.10.209 with commit 6e04a9d30509 Issue introduced in 5.9 with commit cb1a60923609 and fixed in 5.15.148 with commit ff168d4fdb0e Issue introduced in 5.9 with commit cb1a60923609 and fixed in 6.1.75 with commit 63ee7be01a3f Issue introduced in 5.9 with commit cb1a60923609 and fixed in 6.6.14 with commit 763cd6874631 Issue introduced in 5.9 with commit cb1a60923609 and fixed in 6.7.2 with commit 9a662d06c22d Issue introduced in 5.9 with commit cb1a60923609 and fixed in 6.8-rc1 with commit 78d60dae9a0c
This was fixed for Fedora with the 6.6.14 stable kernel updates.