[PATCH AUTOSEL 4.19 375/671] serial: stm32: fix rx data length when parity enabled

Sasha Levin
2020-01-16T18:54:54Z

From: Erwan Le Ray <erwan.leray@st.com>

[ Upstream commit 6c5962f30bce147b1c83869085f3ddde3b34c9e3 ]

- 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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/tty/serial/stm32-usart.c | 12 ++++++++----
drivers/tty/serial/stm32-usart.h | 1 +
2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index f6b739351dde..0a7953e5ce47 100644
--- 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 8d34802e572e..30d2433e27c3 100644
--- 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];
--
2.20.1