[PATCH 1/2] hw/ssi: imx_spi: Correct the burst length > 32 bit transfer logic

[Bin Meng <bmeng.cn@gmail.com>]

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

For the ECSPIx_CONREG register BURST_LENGTH field, the manual says:

0x020 A SPI burst contains the 1 LSB in first word and all 32 bits in second word.
0x021 A SPI burst contains the 2 LSB in first word and all 32 bits in second word.

Current logic uses either s->burst_length or 32, whichever smaller,
to determine how many bits it should read from the tx fifo each time.
For example, for a 48 bit burst length, current logic transfers the
first 32 bit from the first word in the tx fifo, followed by a 16
bit from the second word in the tx fifo, which is wrong. The correct
logic should be: transfer the first 16 bit from the first word in
the tx fifo, followed by a 32 bit from the second word in the tx fifo.

With this change, SPI flash can be successfully probed by U-Boot on
imx6 sabrelite board.

  => sf probe
  SF: Detected sst25vf016b with page size 256 Bytes, erase size 4 KiB, total 2 MiB

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

 hw/ssi/imx_spi.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/hw/ssi/imx_spi.c b/hw/ssi/imx_spi.c
index 85c172e..509fb9f 100644
--- a/hw/ssi/imx_spi.c
+++ b/hw/ssi/imx_spi.c
@@ -178,7 +178,10 @@ static void imx_spi_flush_txfifo(IMXSPIState *s)
 
         DPRINTF("data tx:0x%08x\n", tx);
 
-        tx_burst = MIN(s->burst_length, 32);
+        tx_burst = s->burst_length % 32;
+        if (tx_burst == 0) {
+            tx_burst = 32;
+        }
 
         rx = 0;
 
-- 
2.7.4