serial: stm32: remove infinite loop possibility in putchar function

Rework stm32_usart_console_putchar() function in order to anticipate
the case where the character can never be sent.
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20220419085330.1178925-2-valentin.caron@foss.st.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -1640,10 +1640,16 @@ static void stm32_usart_console_putchar(struct uart_port *port, unsigned char ch
 {
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+	u32 isr;
+	int ret;
 
-	while (!(readl_relaxed(port->membase + ofs->isr) & USART_SR_TXE))
-		cpu_relax();
-
+	ret = readl_relaxed_poll_timeout_atomic(port->membase + ofs->isr, isr,
+						(isr & USART_SR_TXE), 100,
+						STM32_USART_TIMEOUT_USEC);
+	if (ret != 0) {
+		dev_err(port->dev, "Error while sending data in UART TX : %d\n", ret);
+		return;
+	}
 	writel_relaxed(ch, port->membase + ofs->tdr);
 }
 

drivers/tty/serial/stm32-usart.h

@@ -251,6 +251,8 @@ struct stm32_usart_info stm32h7_info = {
 #define RX_BUF_P (RX_BUF_L / 2)	 /* dma rx buffer period     */
 #define TX_BUF_L RX_BUF_L	 /* dma tx buffer length     */
 
+#define STM32_USART_TIMEOUT_USEC USEC_PER_SEC /* 1s timeout in µs */
+
 struct stm32_port {
 	struct uart_port port;
 	struct clk *clk;