spi: fsl-dspi: add cs-gpios support

Make the driver be able to bit-bang a GPIO for the Chip Select pin of
select peripherals.

The GPIO value is driven by the driver in that case, and none of the
hardware Chip Select bits will be populated in the PUSHR register for
the TX commands constructed for this peripheral.

Signed-off-by: Radu Pirea (NXP OSS) <radu-nicolae.pirea@oss.nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20221111211356.545026-1-vladimir.oltean@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

@@ -900,12 +900,31 @@ static irqreturn_t dspi_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+static void dspi_assert_cs(struct spi_device *spi, bool *cs)
+{
+	if (!spi->cs_gpiod || *cs)
+		return;
+
+	gpiod_set_value_cansleep(spi->cs_gpiod, true);
+	*cs = true;
+}
+
+static void dspi_deassert_cs(struct spi_device *spi, bool *cs)
+{
+	if (!spi->cs_gpiod || !*cs)
+		return;
+
+	gpiod_set_value_cansleep(spi->cs_gpiod, false);
+	*cs = false;
+}
+
 static int dspi_transfer_one_message(struct spi_controller *ctlr,
 				     struct spi_message *message)
 {
 	struct fsl_dspi *dspi = spi_controller_get_devdata(ctlr);
 	struct spi_device *spi = message->spi;
 	struct spi_transfer *transfer;
+	bool cs = false;
 	int status = 0;
 
 	message->actual_length = 0;
@@ -914,9 +933,14 @@ static int dspi_transfer_one_message(struct spi_controller *ctlr,
 		dspi->cur_transfer = transfer;
 		dspi->cur_msg = message;
 		dspi->cur_chip = spi_get_ctldata(spi);
+
+		dspi_assert_cs(spi, &cs);
+
 		/* Prepare command word for CMD FIFO */
-		dspi->tx_cmd = SPI_PUSHR_CMD_CTAS(0) |
-			       SPI_PUSHR_CMD_PCS(spi->chip_select);
+		dspi->tx_cmd = SPI_PUSHR_CMD_CTAS(0);
+		if (!spi->cs_gpiod)
+			dspi->tx_cmd |= SPI_PUSHR_CMD_PCS(spi->chip_select);
+
 		if (list_is_last(&dspi->cur_transfer->transfer_list,
 				 &dspi->cur_msg->transfers)) {
 			/* Leave PCS activated after last transfer when
@@ -964,6 +988,9 @@ static int dspi_transfer_one_message(struct spi_controller *ctlr,
 			break;
 
 		spi_transfer_delay_exec(transfer);
+
+		if (!(dspi->tx_cmd & SPI_PUSHR_CMD_CONT))
+			dspi_deassert_cs(spi, &cs);
 	}
 
 	message->status = status;
@@ -981,6 +1008,7 @@ static int dspi_setup(struct spi_device *spi)
 	unsigned char pasc = 0, asc = 0;
 	struct chip_data *chip;
 	unsigned long clkrate;
+	bool cs = true;
 
 	/* Only alloc on first setup */
 	chip = spi_get_ctldata(spi);
@@ -1030,6 +1058,9 @@ static int dspi_setup(struct spi_device *spi)
 			chip->ctar_val |= SPI_CTAR_LSBFE;
 	}
 
+	gpiod_direction_output(spi->cs_gpiod, false);
+	dspi_deassert_cs(spi, &cs);
+
 	spi_set_ctldata(spi, chip);
 
 	return 0;
@@ -1248,6 +1279,7 @@ static int dspi_probe(struct platform_device *pdev)
 	ctlr->cleanup = dspi_cleanup;
 	ctlr->slave_abort = dspi_slave_abort;
 	ctlr->mode_bits = SPI_CPOL | SPI_CPHA | SPI_LSB_FIRST;
+	ctlr->use_gpio_descriptors = true;
 
 	pdata = dev_get_platdata(&pdev->dev);
 	if (pdata) {