stm32h7: support setting bus frequency in SPI driver

Change-Id: I71edf28fdc24d8a00d27aa727815f99e788b675a

firmware/target/arm/stm32/echoplayer/clock-echoplayer.c

@@ -162,3 +162,16 @@ void stm_target_clock_enable(enum stm_clock clock, bool enable)
         break;
     }
 }
+
+size_t stm_target_clock_get_frequency(enum stm_clock clock)
+{
+    switch (clock)
+    {
+    case STM_CLOCK_SPI5_KER:
+        return STM32_HSE_FREQ;
+
+    default:
+        panicf("%s: unsupported clock %d", __func__, (int)clock);
+        return 0;
+    }
+}

firmware/target/arm/stm32/echoplayer/lcd-echoplayer.c

@@ -28,9 +28,13 @@
 #include "regs/stm32h743/rcc.h"
 #include "regs/stm32h743/spi.h"
 
+/* ILI9342C specifies 10 MHz max */
+#define LCD_SPI_FREQ 10000000
+
 struct stm_spi_config spi_cfg = {
     .instance = ITA_SPI5,
     .clock = STM_CLOCK_SPI5_KER,
+    .freq = LCD_SPI_FREQ,
     .mode = STM_SPIMODE_HALF_DUPLEX,
     .proto = STM_SPIPROTO_MOTOROLA,
     .frame_bits = 9,

firmware/target/arm/stm32/spi-stm32h7.c

@@ -108,10 +108,23 @@ static void stm_spi_unpack(void **bufp, size_t *sizep, uint32_t data)
     *sizep = 0;
 }
 
+static uint32_t stm_spi_calc_mbr(const struct stm_spi_config *config)
+{
+    size_t ker_freq = stm_clock_get_frequency(config->clock);
+    for (uint32_t mbr = 0; mbr <= 7; mbr++)
+    {
+        if (ker_freq / (2 << mbr) <= config->freq)
+            return mbr;
+    }
+
+    panicf("%s: impossible frequency", __func__);
+}
+
 void stm_spi_init(struct stm_spi *spi,
                   const struct stm_spi_config *config)
 {
     uint32_t ftlevel;
+    uint32_t mbr = stm_spi_calc_mbr(config);
 
     spi->regs = config->instance;
     spi->clock = config->clock;
@@ -153,7 +166,7 @@ void stm_spi_init(struct stm_spi *spi,
 
     /* TODO: allow setting MBR here */
     reg_writelf(spi->regs, SPI_CFG1,
-                MBR(0),
+                MBR(mbr),
                 CRCEN(0),
                 CRCSIZE(7),
                 TXDMAEN(0),

firmware/target/arm/stm32/spi-stm32h7.h

@@ -50,7 +50,17 @@ struct stm_spi_config
 {
     /* Peripheral instance base address; one of ITA_SPIx */
     uint32_t instance;
+
+    /*
+     * SPI kernel clock and requested SPI bus frequency.
+     * The frequency is used to set the SPI master baud
+     * rate setting based on the kernel clock input, as
+     * such the kernel clock should not be changed after
+     * the SPI peripheral is initialized.
+     */
     enum stm_clock clock;
+    size_t freq;
+
     enum stm_spi_mode mode;
     enum stm_spi_protocol proto;
     stm_spi_set_cs_t set_cs;