serial: stm32: Wait TC bit before performing initialization

In case there is still chars from previous bootstage to transmit, wait
for TC (Transmission Complete) bit to be set which ensure that the last
data written in the USART_TDR has been transmitted out of the shift
register.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>

diff --git a/drivers/serial/serial_stm32.c b/drivers/serial/serial_stm32.c
index 2ba92bf..93f7094 100644 (file)
--- a/drivers/serial/serial_stm32.c
+++ b/drivers/serial/serial_stm32.c
@@ -18,6 +18,7 @@
 #include <dm/device_compat.h>
 #include <linux/bitops.h>
 #include <linux/delay.h>
+#include <linux/iopoll.h>
 #include "serial_stm32.h"
 #include <dm/device_compat.h>
 
@@ -181,9 +182,12 @@ static int stm32_serial_probe(struct udevice *dev)
        struct stm32x7_serial_plat *plat = dev_get_plat(dev);
        struct clk clk;
        struct reset_ctl reset;
+       u32 isr;
        int ret;
+       bool stm32f4;
 
        plat->uart_info = (struct stm32_uart_info *)dev_get_driver_data(dev);
+       stm32f4 = plat->uart_info->stm32f4;
 
        ret = clk_get_by_index(dev, 0, &clk);
        if (ret < 0)
@@ -195,6 +199,17 @@ static int stm32_serial_probe(struct udevice *dev)
                return ret;
        }
 
+       /*
+        * before uart initialization, wait for TC bit (Transmission Complete)
+        * in case there is still chars from previous bootstage to transmit
+        */
+       ret = read_poll_timeout(readl, isr, isr & USART_ISR_TC, 10, 150,
+                               plat->base + ISR_OFFSET(stm32f4));
+       if (ret) {
+               clk_disable(&clk);
+               return ret;
+       }
+
        ret = reset_get_by_index(dev, 0, &reset);
        if (!ret) {
                reset_assert(&reset);

diff --git a/drivers/serial/serial_stm32.h b/drivers/serial/serial_stm32.h
index 5bee68f..b7e7a90 100644 (file)
--- a/drivers/serial/serial_stm32.h
+++ b/drivers/serial/serial_stm32.h
@@ -66,6 +66,7 @@ struct stm32x7_serial_plat {
 #define USART_CR3_OVRDIS               BIT(12)
 
 #define USART_ISR_TXE                  BIT(7)
+#define USART_ISR_TC                   BIT(6)
 #define USART_ISR_RXNE                 BIT(5)
 #define USART_ISR_ORE                  BIT(3)
 #define USART_ISR_FE                   BIT(1)