Blackfin SPI Driver: fix bug - spi controller driver does not assert/deassert CS correctly

This bug can be observed when two SPI devices are sharing the spi bus: One
device is set as SPI CS 7, another one is using SPI CS 4.

In spi_bfin5xx.c: cs_active(), cs_deactive() are used to control SPI_FLG
register.  From the debug bellow:

cs_active: flag: 0x7f91, chip->flag: 0x7f80, cs: 7
cs_active: flag: 0xef91, chip->flag: 0xef10, cs: 4

When device A (cs_7) activate CS 7, SPI_FLG is set as 0x7f91 (however,
SPI_FLG should be set as 0x7f80, or 0x6f91 if in broadcast mode).

Due to some HW bug (very possibly), if SPI_FLG is set as 0x7f91, SPISSEL7
is asserted, however SPISSEL4 will be asserted too (I can see this using
the scope).  This is unreasonable according to HRM.

Signed-off-by: Yi Li <yi.li@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/spi/spi_bfin5xx.c

@@ -189,6 +189,7 @@ static void cs_deactive(struct driver_data *drv_data, struct chip_data *chip)
 {
 	u16 flag = read_FLAG(drv_data);
 
+	flag &= ~chip->flag;
 	flag |= (chip->flag << 8);
 
 	write_FLAG(drv_data, flag);
@@ -1036,7 +1037,6 @@ static int setup(struct spi_device *spi)
 	struct bfin5xx_spi_chip *chip_info = NULL;
 	struct chip_data *chip;
 	struct driver_data *drv_data = spi_master_get_devdata(spi->master);
-	u8 spi_flg;
 
 	/* Abort device setup if requested features are not supported */
 	if (spi->mode & ~(SPI_CPOL | SPI_CPHA | SPI_LSB_FIRST)) {
@@ -1119,8 +1119,7 @@ static int setup(struct spi_device *spi)
 	 * SPI_BAUD, not the real baudrate
 	 */
 	chip->baud = hz_to_spi_baud(spi->max_speed_hz);
-	spi_flg = ~(1 << (spi->chip_select));
-	chip->flag = ((u16) spi_flg << 8) | (1 << (spi->chip_select));
+	chip->flag = 1 << (spi->chip_select);
 	chip->chip_select_num = spi->chip_select;
 
 	switch (chip->bits_per_word) {