spi: orion: enable support for switching CS every transferred byte

Some SPI devices, require toggling the CS every transferred byte.
Enable such possibility in the spi-orion driver.

Note that in order to use it, in the driver of a secondary device
attached to this controller, the SPI bus 'mode' field must be
updated with SPI_CS_WORD flag before calling spi_setup() routine.

In addition to that include a work-around - some devices, such as
certain models of SLIC (Subscriber Line Interface Card),
may require extra delay after CS toggling, so add a minimal
timing relaxation in relevant places.

Signed-off-by: Marcin Wojtas <[e-mail]>
Signed-off-by: Konstantin Porotchkin <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-orion.c

···
 {
 	void __iomem *tx_reg, *rx_reg, *int_reg;
 	struct orion_spi *orion_spi;
+	bool cs_single_byte;
+
+	cs_single_byte = spi->mode & SPI_CS_WORD;
 
 	orion_spi = spi_master_get_devdata(spi->master);
+
+	if (cs_single_byte)
+		orion_spi_set_cs(spi, 0);
+
 	tx_reg = spi_reg(orion_spi, ORION_SPI_DATA_OUT_REG);
 	rx_reg = spi_reg(orion_spi, ORION_SPI_DATA_IN_REG);
 	int_reg = spi_reg(orion_spi, ORION_SPI_INT_CAUSE_REG);
···
 		writel(0, tx_reg);
 
 	if (orion_spi_wait_till_ready(orion_spi) < 0) {
+		if (cs_single_byte) {
+			orion_spi_set_cs(spi, 1);
+			/* Satisfy some SLIC devices requirements */
+			udelay(4);
+		}
 		dev_err(&spi->dev, "TXS timed out\n");
 		return -1;
 	}
 
 	if (rx_buf && *rx_buf)
 		*(*rx_buf)++ = readl(rx_reg);
+
+	if (cs_single_byte) {
+		orion_spi_set_cs(spi, 1);
+		/* Satisfy some SLIC devices requirements */
+		udelay(4);
+	}
 
 	return 1;
 }
···
 {
 	void __iomem *tx_reg, *rx_reg, *int_reg;
 	struct orion_spi *orion_spi;
+
+	if (spi->mode & SPI_CS_WORD) {
+		dev_err(&spi->dev, "SPI_CS_WORD is only supported for 8 bit words\n");
+		return -1;
+	}
 
 	orion_spi = spi_master_get_devdata(spi->master);
 	tx_reg = spi_reg(orion_spi, ORION_SPI_DATA_OUT_REG);
···
 	orion_spi = spi_master_get_devdata(spi->master);
 
 	/*
-	 * Use SPI direct write mode if base address is available. Otherwise
-	 * fall back to PIO mode for this transfer.
+	 * Use SPI direct write mode if base address is available
+	 * and SPI_CS_WORD flag is not set.
+	 * Otherwise fall back to PIO mode for this transfer.
 	 */
 	vaddr = orion_spi->child[cs].direct_access.vaddr;
 
-	if (vaddr && xfer->tx_buf && word_len == 8) {
+	if (vaddr && xfer->tx_buf && word_len == 8 && (spi->mode & SPI_CS_WORD) == 0) {
 		unsigned int cnt = count / 4;
 		unsigned int rem = count % 4;
 
···
 	}
 
 	/* we support all 4 SPI modes and LSB first option */
-	master->mode_bits = SPI_CPHA | SPI_CPOL | SPI_LSB_FIRST;
+	master->mode_bits = SPI_CPHA | SPI_CPOL | SPI_LSB_FIRST | SPI_CS_WORD;
 	master->set_cs = orion_spi_set_cs;
 	master->transfer_one = orion_spi_transfer_one;
 	master->num_chipselect = ORION_NUM_CHIPSELECTS;