Input: ad7877 - implement specified chip select behavior

According to the AD7877 datasheet:

Each transfer operation is 16-bit. If multiple read/write operations are
to be performed, CS must be taken high after the end of each read/write
operation before another read/write operation can be performed by
taking CS low again.

Make sure CS toggles after each transfer in the message.
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/touchscreen/ad7877.c

@@ -230,6 +230,7 @@ static int ad7877_read(struct spi_device *spi, u16 reg)
 			AD7877_READADD(reg));
 	req->xfer[0].tx_buf = &req->command;
 	req->xfer[0].len = 2;
+	req->xfer[0].cs_change = 1;
 
 	req->xfer[1].rx_buf = &req->sample;
 	req->xfer[1].len = 2;
@@ -295,20 +296,25 @@ static int ad7877_read_adc(struct spi_device *spi, unsigned command)
 
 	req->xfer[0].tx_buf = &req->reset;
 	req->xfer[0].len = 2;
+	req->xfer[0].cs_change = 1;
 
 	req->xfer[1].tx_buf = &req->ref_on;
 	req->xfer[1].len = 2;
 	req->xfer[1].delay_usecs = ts->vref_delay_usecs;
+	req->xfer[1].cs_change = 1;
 
 	req->xfer[2].tx_buf = &req->command;
 	req->xfer[2].len = 2;
 	req->xfer[2].delay_usecs = ts->vref_delay_usecs;
+	req->xfer[2].cs_change = 1;
 
 	req->xfer[3].rx_buf = &req->sample;
 	req->xfer[3].len = 2;
+	req->xfer[3].cs_change = 1;
 
 	req->xfer[4].tx_buf = &ts->cmd_crtl2;	/*REF OFF*/
 	req->xfer[4].len = 2;
+	req->xfer[4].cs_change = 1;
 
 	req->xfer[5].tx_buf = &ts->cmd_crtl1;	/*DEFAULT*/
 	req->xfer[5].len = 2;
@@ -640,17 +646,21 @@ static void ad7877_setup_ts_def_msg(struct spi_device *spi, struct ad7877 *ts)
 
 	ts->xfer[0].tx_buf = &ts->cmd_crtl1;
 	ts->xfer[0].len = 2;
+	ts->xfer[0].cs_change = 1;
 
 	spi_message_add_tail(&ts->xfer[0], m);
 
 	ts->xfer[1].tx_buf = &ts->cmd_dummy; /* Send ZERO */
 	ts->xfer[1].len = 2;
+	ts->xfer[1].cs_change = 1;
 
 	spi_message_add_tail(&ts->xfer[1], m);
 
-	for (i = 0; i < 11; i++) {
+	for (i = 0; i < AD7877_NR_SENSE; i++) {
 		ts->xfer[i + 2].rx_buf = &ts->conversion_data[AD7877_SEQ_YPOS + i];
 		ts->xfer[i + 2].len = 2;
+		if (i < (AD7877_NR_SENSE - 1))
+			ts->xfer[i + 2].cs_change = 1;
 		spi_message_add_tail(&ts->xfer[i + 2], m);
 	}
 }