drivers: serial: stm32: always enable clock when exiting low power
Systematically enable the UART clock again when exiting a low power mode
before reading the UART register.
Even though the previous code worked on STM32WBA, for most series, it is
necessary to enable the clock to access the registers, otherwise they read
as 0.
Signed-off-by: Guillaume Gautier <guillaume.gautier-ext@st.com>
diff --git a/drivers/serial/uart_stm32.c b/drivers/serial/uart_stm32.c
index 834012c..a636d88 100644
--- a/drivers/serial/uart_stm32.c
+++ b/drivers/serial/uart_stm32.c
@@ -2081,25 +2081,26 @@
switch (action) {
case PM_DEVICE_ACTION_RESUME:
- /* When exiting low power mode, check whether UART is enabled.
- * If not, it means we are exiting Suspend to RAM mode (STM32
- * Standby), and the driver need to be reinitialized
- */
- if (LL_USART_IsEnabled(config->usart)) {
- /* Set pins to active state */
- err = pinctrl_apply_state(config->pcfg, PINCTRL_STATE_DEFAULT);
- if (err < 0) {
- return err;
- }
+ /* Set pins to active state */
+ err = pinctrl_apply_state(config->pcfg, PINCTRL_STATE_DEFAULT);
+ if (err < 0) {
+ return err;
+ }
- /* enable clock */
- err = clock_control_on(data->clock,
- (clock_control_subsys_t)&config->pclken[0]);
- if (err != 0) {
- LOG_ERR("Could not enable (LP)UART clock");
- return err;
- }
- } else {
+ /* Enable clock */
+ err = clock_control_on(data->clock,
+ (clock_control_subsys_t)&config->pclken[0]);
+ if (err < 0) {
+ LOG_ERR("Could not enable (LP)UART clock");
+ return err;
+ }
+
+ if ((IS_ENABLED(CONFIG_PM_S2RAM)) &&
+ (!LL_USART_IsEnabled(config->usart))) {
+ /* When exiting low power mode, check whether UART is enabled.
+ * If not, it means we are exiting Suspend to RAM mode (STM32
+ * Standby), and the driver needs to be reinitialized.
+ */
uart_stm32_init(dev);
}
break;
@@ -2107,7 +2108,7 @@
uart_stm32_suspend_setup(dev);
/* Stop device clock. Note: fixed clocks are not handled yet. */
err = clock_control_off(data->clock, (clock_control_subsys_t)&config->pclken[0]);
- if (err != 0) {
+ if (err < 0) {
LOG_ERR("Could not enable (LP)UART clock");
return err;
}
