refactor(st-uart): compute the over sampling dynamically

The parameter over_sampling of stm32_uart_init_s is not required
as it can be computed dynamically from clock rate of the serial
device and the requested baudrate.

Oversampling by 8 is allowed only for higher speed
(up to clock_rate / 8) to reduce the maximum receiver tolerance
to clock deviation.

This patch update the driver, the serial init struct and the
only user, the stm32cubeprogrammer over uart support.

Change-Id: I422731089730a288defeb7fa49886db65d0902b2
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>

diff --git a/drivers/st/uart/stm32_uart.c b/drivers/st/uart/stm32_uart.c
index e2e540511cc2566bde801a237cd1e1330bf26837..08bd77b9a24f77aa7df27f4f128c420a0d08bb44 100644 (file)
--- a/drivers/st/uart/stm32_uart.c
+++ b/drivers/st/uart/stm32_uart.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2021-2022, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -106,7 +106,33 @@ static int uart_set_config(struct stm32_uart_handle_s *huart,
 {
        uint32_t tmpreg;
        unsigned long clockfreq;
+       unsigned long int_div;
        uint32_t brrtemp;
+       uint32_t over_sampling;
+
+       /*---------------------- USART BRR configuration --------------------*/
+       clockfreq = uart_get_clock_freq(huart);
+       if (clockfreq == 0UL) {
+               return -ENODEV;
+       }
+
+       int_div = clockfreq / init->baud_rate;
+       if (int_div < 16U) {
+               uint32_t usartdiv = uart_div_sampling8(clockfreq,
+                                                      init->baud_rate,
+                                                      init->prescaler);
+
+               brrtemp = (usartdiv & USART_BRR_DIV_MANTISSA) |
+                         ((usartdiv & USART_BRR_DIV_FRACTION) >> 1);
+               over_sampling = USART_CR1_OVER8;
+       } else {
+               brrtemp = uart_div_sampling16(clockfreq,
+                                             init->baud_rate,
+                                             init->prescaler) &
+                         (USART_BRR_DIV_FRACTION | USART_BRR_DIV_MANTISSA);
+               over_sampling = 0x0U;
+       }
+       mmio_write_32(huart->base + USART_BRR, brrtemp);
 
        /*
         * ---------------------- USART CR1 Configuration --------------------
@@ -115,12 +141,12 @@ static int uart_set_config(struct stm32_uart_handle_s *huart,
         * - set the M bits according to init->word_length value,
         * - set PCE and PS bits according to init->parity value,
         * - set TE and RE bits according to init->mode value,
-        * - set OVER8 bit according to init->over_sampling value.
+        * - set OVER8 bit according baudrate and clock.
         */
        tmpreg = init->word_length |
                 init->parity |
                 init->mode |
-                init->over_sampling |
+                over_sampling |
                 init->fifo_mode;
        mmio_clrsetbits_32(huart->base + USART_CR1, STM32_UART_CR1_FIELDS, tmpreg);
 
@@ -161,27 +187,6 @@ static int uart_set_config(struct stm32_uart_handle_s *huart,
        mmio_clrsetbits_32(huart->base + USART_PRESC, USART_PRESC_PRESCALER,
                           init->prescaler);
 
-       /*---------------------- USART BRR configuration --------------------*/
-       clockfreq = uart_get_clock_freq(huart);
-       if (clockfreq == 0UL) {
-               return -ENODEV;
-       }
-
-       if (init->over_sampling == STM32_UART_OVERSAMPLING_8) {
-               uint32_t usartdiv = uart_div_sampling8(clockfreq,
-                                                      init->baud_rate,
-                                                      init->prescaler);
-
-               brrtemp = (usartdiv & USART_BRR_DIV_MANTISSA) |
-                         ((usartdiv & USART_BRR_DIV_FRACTION) >> 1);
-       } else {
-               brrtemp = uart_div_sampling16(clockfreq,
-                                             init->baud_rate,
-                                             init->prescaler) &
-                         (USART_BRR_DIV_FRACTION | USART_BRR_DIV_MANTISSA);
-       }
-       mmio_write_32(huart->base + USART_BRR, brrtemp);
-
        return 0;
 }
 

diff --git a/include/drivers/st/stm32_uart.h b/include/drivers/st/stm32_uart.h
index 212968f57db149ca554f7e0273de6cf4ee951c68..866e1589072e4c10871edf7db9f72448ded572dc 100644 (file)
--- a/include/drivers/st/stm32_uart.h
+++ b/include/drivers/st/stm32_uart.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2021-2022, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -34,10 +34,6 @@
 #define STM32_UART_HWCONTROL_CTS               USART_CR3_CTSE
 #define STM32_UART_HWCONTROL_RTS_CTS           (USART_CR3_RTSE | USART_CR3_CTSE)
 
-/* UART over sampling */
-#define STM32_UART_OVERSAMPLING_16             0x00000000U
-#define STM32_UART_OVERSAMPLING_8              USART_CR1_OVER8
-
 /* UART prescaler */
 #define STM32_UART_PRESCALER_DIV1              0x00000000U
 #define STM32_UART_PRESCALER_DIV2              0x00000001U
@@ -112,13 +108,6 @@ struct stm32_uart_init_s {
                                         * value of @ref STM32_UARTHWCONTROL_*.
                                         */
 
-       uint32_t over_sampling;         /*
-                                        * Specifies whether the over sampling
-                                        * 8 is enabled or disabled.
-                                        * This parameter can be a value of
-                                        * @ref STM32_UART_OVERSAMPLING_*.
-                                        */
-
        uint32_t one_bit_sampling;      /*
                                         * Specifies whether a single sample
                                         * or three samples' majority vote is

diff --git a/plat/st/common/stm32cubeprogrammer_uart.c b/plat/st/common/stm32cubeprogrammer_uart.c
index 46ac9cf174e0db7264980c211e013df27991174f..95207030c36746e0ee337f3b96bc711015fb19e8 100644 (file)
--- a/plat/st/common/stm32cubeprogrammer_uart.c
+++ b/plat/st/common/stm32cubeprogrammer_uart.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2021-2022, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -492,7 +492,6 @@ const struct stm32_uart_init_s init = {
        .parity = STM32_UART_PARITY_EVEN,
        .hw_flow_control = STM32_UART_HWCONTROL_NONE,
        .mode = STM32_UART_MODE_TX_RX,
-       .over_sampling = STM32_UART_OVERSAMPLING_16,
        .fifo_mode = STM32_UART_FIFOMODE_EN,
 };