staging: mt7621-spi: drop support for SPI mode 1/2/3

As explained in previous patch, this SPI controller seems to be
tested on SPI flash only before mass production and some bits are
swizzled under other SPI modes probably due to incorrect wiring
inside the silicon. Drop implementation of SPI mode 1/2/3 since
they are broken.

Also drop RT2880_SPI_MODE_BITS macro because we now have only
SPI_LSB_FIRST implemented and the mode_bits is so short that we
don't need a macro there.
Signed-off-by: Chuanhong Guo <gch981213@gmail.com>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-spi/spi-mt7621.c

@@ -55,9 +55,6 @@
 #define MT7621_CPOL		BIT(4)
 #define MT7621_LSB_FIRST	BIT(3)
 
-#define RT2880_SPI_MODE_BITS	(SPI_CPOL | SPI_CPHA |		\
-				 SPI_LSB_FIRST | SPI_CS_HIGH)
-
 struct mt7621_spi;
 
 struct mt7621_spi {
@@ -136,20 +133,13 @@ static int mt7621_spi_prepare(struct spi_device *spi, unsigned int speed)
 	if (spi->mode & SPI_LSB_FIRST)
 		reg |= MT7621_LSB_FIRST;
 
+	/* This SPI controller seems to be tested on SPI flash only
+	 * and some bits are swizzled under other SPI modes probably
+	 * due to incorrect wiring inside the silicon. Only mode 0
+	 * works correctly.
+	 */
 	reg &= ~(MT7621_CPHA | MT7621_CPOL);
-	switch (spi->mode & (SPI_CPOL | SPI_CPHA)) {
-	case SPI_MODE_0:
-		break;
-	case SPI_MODE_1:
-		reg |= MT7621_CPHA;
-		break;
-	case SPI_MODE_2:
-		reg |= MT7621_CPOL;
-		break;
-	case SPI_MODE_3:
-		reg |= MT7621_CPOL | MT7621_CPHA;
-		break;
-	}
+
 	mt7621_spi_write(rs, MT7621_SPI_MASTER, reg);
 
 	return 0;
@@ -368,7 +358,7 @@ static int mt7621_spi_probe(struct platform_device *pdev)
 		return -ENOMEM;
 	}
 
-	master->mode_bits = RT2880_SPI_MODE_BITS;
+	master->mode_bits = SPI_LSB_FIRST;
 
 	master->setup = mt7621_spi_setup;
 	master->transfer_one_message = mt7621_spi_transfer_one_message;