staging: mt7621-spi: drop the broken full-duplex mode

According to John Crispin (aka blogic) on IRC on Nov 26 2018:
  so basically i made cs1 work for MTK/labs when i built
  the linkit smart for them. the req-sheet said that cs1 should be proper
  duplex spi. however ....
   1) the core will always send 1 byte before any transfer, this is the
      m25p80 command.
   2) mode 3 is broken and bit reversed (?)
   3) some bit are incorrectly wired in hw for mode2/3
  we wrote a test script and test for [0-0xffff] on all modes and certain
  bits are swizzled under certain conditions and it was not possible to
  fix this even using a hack.
  we then decided to use spi-gpio and i never removed the errornous code
  basically the spi is fecked for anything but half duplex spi mode0
  running a sflash on it

The controller will always send some data from OPCODE register under half
duplex mode before starting a full-duplex transfer, so the full-duplex
mode is broken.
This piece of code also make CS1 unavailable since it forces the
broken full-duplex mode to be used on CS1.
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

@@ -86,15 +86,12 @@ static inline void mt7621_spi_write(struct mt7621_spi *rs, u32 reg, u32 val)
 	iowrite32(val, rs->base + reg);
 }
 
-static void mt7621_spi_reset(struct mt7621_spi *rs, int duplex)
+static void mt7621_spi_reset(struct mt7621_spi *rs)
 {
 	u32 master = mt7621_spi_read(rs, MT7621_SPI_MASTER);
 
 	master |= 7 << 29;
 	master |= 1 << 2;
-	if (duplex)
-		master |= 1 << 10;
-	else
 	master &= ~(1 << 10);
 
 	mt7621_spi_write(rs, MT7621_SPI_MASTER, master);
@@ -107,7 +104,7 @@ static void mt7621_spi_set_cs(struct spi_device *spi, int enable)
 	int cs = spi->chip_select;
 	u32 polar = 0;
 
-	mt7621_spi_reset(rs, cs);
+	mt7621_spi_reset(rs);
 	if (enable)
 		polar = BIT(cs);
 	mt7621_spi_write(rs, MT7621_SPI_POLAR, polar);
@@ -261,7 +258,7 @@ static void mt7621_spi_write_half_duplex(struct mt7621_spi *rs,
 	rs->pending_write = len;
 }
 
-static int mt7621_spi_transfer_half_duplex(struct spi_master *master,
+static int mt7621_spi_transfer_one_message(struct spi_master *master,
 					   struct spi_message *m)
 {
 	struct mt7621_spi *rs = spi_master_get_devdata(master);
@@ -284,10 +281,20 @@ static int mt7621_spi_transfer_half_duplex(struct spi_master *master,
 	mt7621_spi_set_cs(spi, 1);
 	m->actual_length = 0;
 	list_for_each_entry(t, &m->transfers, transfer_list) {
-		if (t->rx_buf)
+		if ((t->rx_buf) && (t->tx_buf)) {
+			/* This controller will shift some extra data out
+			 * of spi_opcode if (mosi_bit_cnt > 0) &&
+			 * (cmd_bit_cnt == 0). So the claimed full-duplex
+			 * support is broken since we have no way to read
+			 * the MISO value during that bit.
+			 */
+			status = -EIO;
+			goto msg_done;
+		} else if (t->rx_buf) {
 			mt7621_spi_read_half_duplex(rs, t->len, t->rx_buf);
-		else if (t->tx_buf)
+		} else if (t->tx_buf) {
 			mt7621_spi_write_half_duplex(rs, t->len, t->tx_buf);
+		}
 		m->actual_length += t->len;
 	}
 	mt7621_spi_flush(rs);
@@ -300,102 +307,6 @@ static int mt7621_spi_transfer_half_duplex(struct spi_master *master,
 	return 0;
 }
 
-static int mt7621_spi_transfer_full_duplex(struct spi_master *master,
-					   struct spi_message *m)
-{
-	struct mt7621_spi *rs = spi_master_get_devdata(master);
-	struct spi_device *spi = m->spi;
-	unsigned int speed = spi->max_speed_hz;
-	struct spi_transfer *t = NULL;
-	int status = 0;
-	int i, len = 0;
-	int rx_len = 0;
-	u32 data[9] = { 0 };
-	u32 val = 0;
-
-	mt7621_spi_wait_till_ready(rs);
-
-	list_for_each_entry(t, &m->transfers, transfer_list) {
-		const u8 *buf = t->tx_buf;
-
-		if (t->rx_buf)
-			rx_len += t->len;
-
-		if (!buf)
-			continue;
-
-		if (WARN_ON(len + t->len > 16)) {
-			status = -EIO;
-			goto msg_done;
-		}
-
-		for (i = 0; i < t->len; i++, len++)
-			data[len / 4] |= buf[i] << (8 * (len & 3));
-		if (speed > t->speed_hz)
-			speed = t->speed_hz;
-	}
-
-	if (WARN_ON(rx_len > 16)) {
-		status = -EIO;
-		goto msg_done;
-	}
-
-	if (mt7621_spi_prepare(spi, speed)) {
-		status = -EIO;
-		goto msg_done;
-	}
-
-	for (i = 0; i < len; i += 4)
-		mt7621_spi_write(rs, MT7621_SPI_DATA0 + i, data[i / 4]);
-
-	val |= len * 8;
-	val |= (rx_len * 8) << 12;
-	mt7621_spi_write(rs, MT7621_SPI_MOREBUF, val);
-
-	mt7621_spi_set_cs(spi, 1);
-
-	val = mt7621_spi_read(rs, MT7621_SPI_TRANS);
-	val |= SPI_CTL_START;
-	mt7621_spi_write(rs, MT7621_SPI_TRANS, val);
-
-	mt7621_spi_wait_till_ready(rs);
-
-	mt7621_spi_set_cs(spi, 0);
-
-	for (i = 0; i < rx_len; i += 4)
-		data[i / 4] = mt7621_spi_read(rs, MT7621_SPI_DATA4 + i);
-
-	m->actual_length = rx_len;
-
-	len = 0;
-	list_for_each_entry(t, &m->transfers, transfer_list) {
-		u8 *buf = t->rx_buf;
-
-		if (!buf)
-			continue;
-
-		for (i = 0; i < t->len; i++, len++)
-			buf[i] = data[len / 4] >> (8 * (len & 3));
-	}
-
-msg_done:
-	m->status = status;
-	spi_finalize_current_message(master);
-
-	return 0;
-}
-
-static int mt7621_spi_transfer_one_message(struct spi_master *master,
-					   struct spi_message *m)
-{
-	struct spi_device *spi = m->spi;
-	int cs = spi->chip_select;
-
-	if (cs)
-		return mt7621_spi_transfer_full_duplex(master, m);
-	return mt7621_spi_transfer_half_duplex(master, m);
-}
-
 static int mt7621_spi_setup(struct spi_device *spi)
 {
 	struct mt7621_spi *rs = spidev_to_mt7621_spi(spi);
@@ -478,7 +389,7 @@ static int mt7621_spi_probe(struct platform_device *pdev)
 
 	device_reset(&pdev->dev);
 
-	mt7621_spi_reset(rs, 0);
+	mt7621_spi_reset(rs);
 
 	return spi_register_master(master);
 }