On 14.01.2022 04:08, Tim Harvey wrote: > So I believe in order to support using gpios for rts/cts in the imx > uart driver I must find the right place to call imx_uart_rts_active > and imx_uart_rts_inactive when the FIFO is not full and full > respectively. I'm not that familiar with the Linux uart driver > framework - am I on the right track and if so any ideas where this is > best done? It is not really the driver (and thus FIFO level), but rather the amount of free space in tty buffer (checked by Line Discipline workqueue) that determines when to throttle (set RTS inactive). This mostly works fine, but fails [1] when the RX interrupt frequency is too high [2]. The throttle/unthrottle request, when termios CRTSCTS is set, is seen by the driver as the call to .set_mctrl (imx_uart_set_mctrl) with TIOCM_RTS bit cleared/set in mctrl parameter. Currently imx_uart_set_mctrl() only controls the UCR2_CTS and UCR2_CTSC bits based on mctrl. To support your case you would most likely have to add the gpio handling in imx_uart_set_mctrl(). However, I am unaware what other issues you might encounter (i.e. if it is not done there yet simply because nobody had that use case or if there is some deeper problem). [1] https://lore.kernel.org/linux-serial/10e723c0-a28b-de0d-0632-0bd250478313@xxxxxxxxxxxxxxx/ [2] https://lore.kernel.org/linux-serial/20220104103203.2033673-1-tomasz.mon@xxxxxxxxxxxxxxx/ Best Regards, Tomasz Mon
