commit 2bed8a8e70 upstream.
When in RS485 emulation mode, __do_stop_tx_rs485() calls
serial8250_clear_fifos(). This not only clears the FIFOs, but also sets
all bits in their control register (UART_FCR) to 0.
One of the effects of this is the disabling of the FIFOs, which turns
them into single-byte holding registers. The rest of the driver doesn't
know this, which results in the lions share of characters passed into a
write call to be dropped.
(I can supply logic analyzer screenshots if necessary)
This fix replaces the serial8250_clear_fifos() call to
serial8250_clear_and_reinit_fifos() - this prevents the "dropped
characters" issue from manifesting again while retaining the requirement
of clearing the RX FIFO after transmission if the SER_RS485_RX_DURING_TX
flag is disabled.
Signed-off-by: Daniel Jedrychowski <avistel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
eca02f01be