[PATCH] serial: xilinx_uartps: fix rs485 delay_rts_after_send

[j.turek]

RTS line control with delay should be triggered when there is no more bytes
in kfifo and hardware buffer is empty. Without this patch RTS control is
scheduled right after feeding hardware buffer and this is too early.
RTS line may change state before hardware buffer is empty.
With this patch delayed RTS state change is triggered when function
cdns_uart_handle_tx is called from cdns_uart_isr on CDNS_UART_IXR_TXEMPTY
exactly when hardware completed transmission

Signed-off-by: Jakub Turek  <jakub.turek at elsta.tech>

Fixes: fccc9d9233f9 ("tty: serial: uartps: Add rs485 support to uartps driver")
---
 drivers/tty/serial/xilinx_uartps.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 1e4d54fd5762..923a8b57ec82 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -432,6 +432,12 @@ static void cdns_uart_handle_tx(void *dev_id)
 	if (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(port)) {
 		/* Disable the TX Empty interrupt */
 		writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_IDR);
+		/* Set RTS line after delay */
+		if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED) {
+			cdns_uart->tx_timer.function = &cdns_rs485_rx_callback;
+			rts_delay = ns_to_ktime(cdns_calc_after_tx_delay(cdns_uart));
+			hrtimer_start(&cdns_uart->tx_timer, rts_delay, HRTIMER_MODE_REL);
+		}
 		return;
 	}
 
@@ -448,13 +454,6 @@ static void cdns_uart_handle_tx(void *dev_id)
 
 	/* Enable the TX Empty interrupt */
 	writel(CDNS_UART_IXR_TXEMPTY, cdns_uart->port->membase + CDNS_UART_IER);
-
-	if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED &&
-	    (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(port))) {
-		hrtimer_update_function(&cdns_uart->tx_timer, cdns_rs485_rx_callback);
-		hrtimer_start(&cdns_uart->tx_timer,
-			      ns_to_ktime(cdns_calc_after_tx_delay(cdns_uart)), HRTIMER_MODE_REL);
-	}
 }
 
 /**
-- 
2.34.1