Using a loopback serial cable with RS485 protocol shows that data is received: $ stty -F /dev/ttyS3 raw -echo speed 4800 $ cat /dev/ttyS3 & $ echo "Hello, world" > /dev/ttyS3 Hello, world Last line should not be displayed, as it indicates that RX was started before TX finished. This happens because driver activates RX when the DMA transfer completes, but that does not necessarily mean the TX FIFO was emptied. First patch will add a helper that checks if the transmission is half-duplex and uses it throughout the driver, replacing multiple lines of code. Second patch implements the fix by adding a variable to the port struct. This is used to indicate that RX needs to be started. When the DMA transfer completes, the variable is set and the ATMEL_US_TXEMPTY is reactivated. In the interrupt handler, if the variable is set, RX is started. Changelog: v1 -> v2: - remove wrongly added check; - start rx and display warning message in case of error - add fix info Razvan Stefanescu (2): tty/serial: atmel: Add is_half_duplex helper tty/serial: atmel: RS485 HD w/DMA: enable RX after TX is stopped drivers/tty/serial/atmel_serial.c | 48 +++++++++++++++++++++---------- 1 file changed, 33 insertions(+), 15 deletions(-) -- 2.19.1
