[PATCH v2 4/4] hw/ssi: imx_spi: Correct tx and rx fifo endianness

[Bin Meng]

From: Bin Meng <bin.meng@windriver.com>

The endianness of data exchange between tx and rx fifo is incorrect.
Earlier bytes are supposed to show up on MSB and later bytes on LSB,
ie: in big endian. The manual does not explicitly say this, but the
U-Boot and Linux driver codes have a swap on the data transferred
to tx fifo and from rx fifo.

With this change, U-Boot read from / write to SPI flash tests pass.

  => sf test 1ff000 1000
  SPI flash test:
  0 erase: 0 ticks, 4096000 KiB/s 32768.000 Mbps
  1 check: 3 ticks, 1333 KiB/s 10.664 Mbps
  2 write: 235 ticks, 17 KiB/s 0.136 Mbps
  3 read: 2 ticks, 2000 KiB/s 16.000 Mbps
  Test passed
  0 erase: 0 ticks, 4096000 KiB/s 32768.000 Mbps
  1 check: 3 ticks, 1333 KiB/s 10.664 Mbps
  2 write: 235 ticks, 17 KiB/s 0.136 Mbps
  3 read: 2 ticks, 2000 KiB/s 16.000 Mbps

Fixes: c906a3a01582 ("i.MX: Add the Freescale SPI Controller")
Signed-off-by: Bin Meng <bin.meng@windriver.com>

---

(no changes since v1)

 hw/ssi/imx_spi.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/hw/ssi/imx_spi.c b/hw/ssi/imx_spi.c
index 0cf07d295c..d45aaae320 100644
--- a/hw/ssi/imx_spi.c
+++ b/hw/ssi/imx_spi.c
@@ -156,13 +156,14 @@ static void imx_spi_flush_txfifo(IMXSPIState *s)
 {
     uint32_t tx;
     uint32_t rx;
+    uint32_t data;
+    uint8_t byte;
 
     DPRINTF("Begin: TX Fifo Size = %d, RX Fifo Size = %d\n",
             fifo32_num_used(&s->tx_fifo), fifo32_num_used(&s->rx_fifo));
 
     while (!fifo32_is_empty(&s->tx_fifo)) {
         int tx_burst = 0;
-        int index = 0;
 
         if (s->burst_length <= 0) {
             s->burst_length = imx_spi_burst_length(s);
@@ -180,10 +181,18 @@ static void imx_spi_flush_txfifo(IMXSPIState *s)
 
         tx_burst = (s->burst_length % 32) ? : 32;
 
+        data = 0;
+        for (int i = 0; i < tx_burst / 8; i++) {
+            byte = tx & 0xff;
+            tx = tx >> 8;
+            data = (data << 8) | byte;
+        }
+        tx = data;
+
         rx = 0;
 
         while (tx_burst > 0) {
-            uint8_t byte = tx & 0xff;
+            byte = tx & 0xff;
 
             DPRINTF("writing 0x%02x\n", (uint32_t)byte);
 
@@ -193,12 +202,11 @@ static void imx_spi_flush_txfifo(IMXSPIState *s)
             DPRINTF("0x%02x read\n", (uint32_t)byte);
 
             tx = tx >> 8;
-            rx |= (byte << (index * 8));
+            rx = (rx << 8) | byte;
 
             /* Remove 8 bits from the actual burst */
             tx_burst -= 8;
             s->burst_length -= 8;
-            index++;
         }
 
         DPRINTF("data rx:0x%08x\n", rx);
-- 
2.25.1