Merge pull request ARMmbed#10804 from VVESTM/vve_fix_10589

TARGET_STM: SPI: update pull up config depending on clk polarity

Author: 0xc0170

targets/TARGET_STM/stm_spi_api.c

@@ -216,6 +216,12 @@ void spi_init(spi_t *obj, PinName mosi, PinName miso, PinName sclk, PinName ssel
     handle->Init.FifoThreshold     = SPI_FIFO_THRESHOLD_01DATA;
 #endif
 
+    /*
+    * According the STM32 Datasheet for SPI peripheral we need to PULLDOWN
+    * or PULLUP the SCK pin according the polarity used.
+    */
+    pin_mode(spiobj->pin_sclk, (handle->Init.CLKPolarity == SPI_POLARITY_LOW) ? PullDown: PullUp);
+
     init_spi(obj);
 }
 
@@ -290,6 +296,7 @@ void spi_format(spi_t *obj, int bits, int mode, int slave)
 {
     struct spi_s *spiobj = SPI_S(obj);
     SPI_HandleTypeDef *handle = &(spiobj->handle);
+    PinMode pull = 0;
 
     DEBUG_PRINTF("spi_format, bits:%d, mode:%d, slave?:%d\r\n", bits, mode, slave);
 
@@ -331,6 +338,13 @@ void spi_format(spi_t *obj, int bits, int mode, int slave)
         handle->Init.Direction = SPI_DIRECTION_2LINES;
     }
 
+    /*
+    * According the STM32 Datasheet for SPI peripheral we need to PULLDOWN
+    * or PULLUP the SCK pin according the polarity used.
+    */
+    pull = (handle->Init.CLKPolarity == SPI_POLARITY_LOW) ? PullDown: PullUp;
+    pin_mode(spiobj->pin_sclk, pull);
+
     init_spi(obj);
 }