spi/bfin_spi: warn when CS is driven by hardware (CPHA=0)

When the hardware is controlling the CS, there are some SPI options
we are unable to support.  So issue a warning in the hopes that the
user will change to a SPI mode where we can support things sanely.

Signed-off-by: Barry Song <barry.song@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

drivers/spi/spi_bfin5xx.c

@@ -1040,9 +1040,14 @@ static int bfin_spi_setup(struct spi_device *spi)
 	 */
 	chip->baud = hz_to_spi_baud(spi->max_speed_hz);
 	chip->chip_select_num = spi->chip_select;
-	if (chip->chip_select_num < MAX_CTRL_CS)
+	if (chip->chip_select_num < MAX_CTRL_CS) {
+		if (!(spi->mode & SPI_CPHA))
+			dev_warn(&spi->dev, "Warning: SPI CPHA not set:"
+				" Slave Select not under software control!\n"
+				" See Documentation/blackfin/bfin-spi-notes.txt");
+
 		chip->flag = (1 << spi->chip_select) << 8;
-	else
+	} else
 		chip->cs_gpio = chip->chip_select_num - MAX_CTRL_CS;
 
 	if (chip->enable_dma && chip->pio_interrupt) {