imx_set_termios(): avoid writing baud rate divider registers when the
values to be written are the same as current. Any writing seems to
restart transmission/receiving logic in the hardware, that leads to
data breakage even when rate doesn't in fact change. E.g., user
switches RTS/CTS handshake and suddenly gets broken bytes.
Signed-off-by: Sergey Organov <sorganov@xxxxxxxxx>
---
drivers/tty/serial/imx.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 4b9c560..db3fb4c 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1537,7 +1537,7 @@ imx_uart_set_termios(struct uart_port *port, struct ktermios *termios,
unsigned int baud, quot;
unsigned int old_csize = old ? old->c_cflag & CSIZE : CS8;
unsigned long div;
- unsigned long num, denom;
+ unsigned long num, denom, old_ubir, old_ubmr;
uint64_t tdiv64;
/*
@@ -1660,8 +1660,21 @@ imx_uart_set_termios(struct uart_port *port, struct ktermios *termios,
ufcr = (ufcr & (~UFCR_RFDIV)) | UFCR_RFDIV_REG(div);
imx_uart_writel(sport, ufcr, UFCR);
- imx_uart_writel(sport, num, UBIR);
- imx_uart_writel(sport, denom, UBMR);
+ /*
+ * Two registers below should always be written both and in this
+ * particular order. One consequence is that we need to check if any of
+ * them changes and then update both. We do need the check for change
+ * as even writing the same values seem to "restart"
+ * transmission/receiving logic in the hardware, that leads to data
+ * breakage even when rate doesn't in fact change. E.g., user switches
+ * RTS/CTS handshake and suddenly gets broken bytes.
+ */
+ old_ubir = imx_uart_readl(sport, UBIR);
+ old_ubmr = imx_uart_readl(sport, UBMR);
+ if (old_ubir != num || old_ubmr != denom) {
+ imx_uart_writel(sport, num, UBIR);
+ imx_uart_writel(sport, denom, UBMR);
+ }
if (!imx_uart_is_imx1(sport))
imx_uart_writel(sport, sport->port.uartclk / div / 1000,
--
2.10.0.1.g57b01a3
