[PATCH v2 8/9] serial: stm32-usart: Correct CSIZE, bits, and parity

[Ilpo Järvinen]

Add CSIZE sanitization for unsupported CSIZE configurations. In
addition, if parity is asked for but CSx was unsupported, the sensible
result is CS8+parity which requires setting USART_CR1_M0 like with 9
bits.

Incorrect CSIZE results in miscalculation of the frame bits in
tty_get_char_size() or in its predecessor where the roughly the same
code is directly within uart_update_timeout().

Cc: Erwan Le Ray <erwan.leray at st.com>
Fixes: c8a9d043947b (serial: stm32: fix word length configuration)
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen at linux.intel.com>
---
 drivers/tty/serial/stm32-usart.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 87b5cd4c9743..3c551fd4f3ff 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -1037,13 +1037,22 @@ static void stm32_usart_set_termios(struct uart_port *port,
 	 * CS8 or (CS7 + parity), 8 bits word aka [M1:M0] = 0b00
 	 * M0 and M1 already cleared by cr1 initialization.
 	 */
-	if (bits == 9)
+	if (bits == 9) {
 		cr1 |= USART_CR1_M0;
-	else if ((bits == 7) && cfg->has_7bits_data)
+	} else if ((bits == 7) && cfg->has_7bits_data) {
 		cr1 |= USART_CR1_M1;
-	else if (bits != 8)
+	} else if (bits != 8) {
 		dev_dbg(port->dev, "Unsupported data bits config: %u bits\n"
 			, bits);
+		cflag &= ~CSIZE;
+		cflag |= CS8;
+		termios->c_cflag = cflag;
+		bits = 8;
+		if (cflag & PARENB) {
+			bits++;
+			cr1 |= USART_CR1_M0;
+		}
+	}
 
 	if (ofs->rtor != UNDEF_REG && (stm32_port->rx_ch ||
 				       (stm32_port->fifoen &&
-- 
2.30.2