drivers: fpga: fix waveform for iCE40 configuration in SPI mode

The datasheet of the iCE40 specifies that there should be a leading and
trailing clocks phase during its configuration with SPI. Due to the
limitations of the SPI interface, and probably also due to a lock of
support for such a feature for instance in the STM32 SPI peripheral,
this is achieved with additional SPI transfers before and after the
actual image. Unfortunately, this by default also affects the slave
select GPIO, which has to stay high during these phases.
This fixes this behaviour via not passing the slave select GPIO
to the SPI driver and manipulating this GPIO manually.

Signed-off-by: Benedikt Schmidt <benedikt.schmidt@embedded-solutions.at>

drivers/fpga/fpga_ice40.c

@@ -317,6 +317,15 @@ static int fpga_ice40_load_spi(const struct device *dev, uint32_t *image_ptr, ui
 	struct fpga_ice40_data *data = dev->data;
 	uint8_t clock_buf[(UINT8_MAX + 1) / BITS_PER_BYTE];
 	const struct fpga_ice40_config *config = dev->config;
+	struct spi_dt_spec bus;
+
+	memcpy(&bus, &config->bus, sizeof(bus));
+	/*
+	 * Disable the automatism for chip select within the SPI driver,
+	 * as the configuration sequence requires this signal to be inactive
+	 * during the leading and trailing clock phase.
+	 */
+	bus.config.cs.gpio.port = NULL;
 
 	/* crc check */
 	crc = crc32_ieee((uint8_t *)image_ptr, img_size);
@@ -381,7 +390,7 @@ static int fpga_ice40_load_spi(const struct device *dev, uint32_t *image_ptr, ui
 	LOG_DBG("Send %u clocks", config->leading_clocks);
 	tx_buf.buf = clock_buf;
 	tx_buf.len = DIV_ROUND_UP(config->leading_clocks, BITS_PER_BYTE);
-	ret = spi_write_dt(&config->bus, &tx_bufs);
+	ret = spi_write_dt(&bus, &tx_bufs);
 	if (ret < 0) {
 		LOG_ERR("Failed to send leading %u clocks: %d", config->leading_clocks, ret);
 		goto unlock;
@@ -397,7 +406,7 @@ static int fpga_ice40_load_spi(const struct device *dev, uint32_t *image_ptr, ui
 	LOG_DBG("Send bin file");
 	tx_buf.buf = image_ptr;
 	tx_buf.len = img_size;
-	ret = spi_write_dt(&config->bus, &tx_bufs);
+	ret = spi_write_dt(&bus, &tx_bufs);
 	if (ret < 0) {
 		LOG_ERR("Failed to send bin file: %d", ret);
 		goto unlock;
@@ -413,7 +422,7 @@ static int fpga_ice40_load_spi(const struct device *dev, uint32_t *image_ptr, ui
 	LOG_DBG("Send %u clocks", config->trailing_clocks);
 	tx_buf.buf = clock_buf;
 	tx_buf.len = DIV_ROUND_UP(config->trailing_clocks, BITS_PER_BYTE);
-	ret = spi_write_dt(&config->bus, &tx_bufs);
+	ret = spi_write_dt(&bus, &tx_bufs);
 	if (ret < 0) {
 		LOG_ERR("Failed to send trailing %u clocks: %d", config->trailing_clocks, ret);
 		goto unlock;
@@ -596,7 +605,10 @@ static int fpga_ice40_init(const struct device *dev)
 	static struct fpga_ice40_data fpga_ice40_data_##inst;                                      \
                                                                                                    \
 	static const struct fpga_ice40_config fpga_ice40_config_##inst = {                         \
-		.bus = SPI_DT_SPEC_INST_GET(inst, SPI_WORD_SET(8) | SPI_TRANSFER_MSB, 0),          \
+		.bus = SPI_DT_SPEC_INST_GET(inst,                                                  \
+					    SPI_OP_MODE_MASTER | SPI_MODE_CPOL | SPI_MODE_CPHA |   \
+						    SPI_WORD_SET(8) | SPI_TRANSFER_MSB,            \
+					    0),                                                    \
 		.creset = GPIO_DT_SPEC_INST_GET(inst, creset_gpios),                               \
 		.cdone = GPIO_DT_SPEC_INST_GET(inst, cdone_gpios),                                 \
 		.clk = GPIO_DT_SPEC_INST_GET_OR(inst, clk_gpios, {0}),                             \