serial: stm32: fix rx data length when parity enabled

- Fixes a rx data error when data length < 8 bits and parity is enabled.
RDR register MSB is used for parity bit reception.
- Adds a mask to ignore MSB when data is get from RDR.

Fixes: 3489187204eb ("serial: stm32: adding dma support")
Signed-off-by: Erwan Le Ray <erwan.leray@st.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index f6b7393..0a7953e 100644 (file)
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -194,8 +194,8 @@ static int stm32_pending_rx(struct uart_port *port, u32 *sr, int *last_res,
        return 0;
 }
 
-static unsigned long
-stm32_get_char(struct uart_port *port, u32 *sr, int *last_res)
+static unsigned long stm32_get_char(struct uart_port *port, u32 *sr,
+                                   int *last_res)
 {
        struct stm32_port *stm32_port = to_stm32_port(port);
        struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
@@ -205,10 +205,13 @@ stm32_get_char(struct uart_port *port, u32 *sr, int *last_res)
                c = stm32_port->rx_buf[RX_BUF_L - (*last_res)--];
                if ((*last_res) == 0)
                        *last_res = RX_BUF_L;
-               return c;
        } else {
-               return readl_relaxed(port->membase + ofs->rdr);
+               c = readl_relaxed(port->membase + ofs->rdr);
+               /* apply RDR data mask */
+               c &= stm32_port->rdr_mask;
        }
+
+       return c;
 }
 
 static void stm32_receive_chars(struct uart_port *port, bool threaded)
@@ -679,6 +682,7 @@ static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
                cr2 |= USART_CR2_STOP_2B;
 
        bits = stm32_get_databits(termios);
+       stm32_port->rdr_mask = (BIT(bits) - 1);
 
        if (cflag & PARENB) {
                bits++;

diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index 8d34802..30d2433 100644 (file)
--- a/drivers/tty/serial/stm32-usart.h
+++ b/drivers/tty/serial/stm32-usart.h
@@ -254,6 +254,7 @@ struct stm32_port {
        bool hw_flow_control;
        bool fifoen;
        int wakeirq;
+       int rdr_mask;           /* receive data register mask */
 };
 
 static struct stm32_port stm32_ports[STM32_MAX_PORTS];