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>

diff --git a/drivers/staging/mt7621-spi/spi-mt7621.c b/drivers/staging/mt7621-spi/spi-mt7621.c
index d045b5568e0f83b485db7102e18d2805764bd9d7..a69293d43281df4e535913fc53e74ca4c0138731 100644 (file)
--- a/drivers/staging/mt7621-spi/spi-mt7621.c
+++ b/drivers/staging/mt7621-spi/spi-mt7621.c
@@ -86,16 +86,13 @@ 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);
+       master &= ~(1 << 10);
 
        mt7621_spi_write(rs, MT7621_SPI_MASTER, master);
        rs->pending_write = 0;
@@ -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 @@ msg_done:
        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);
 }