spi: dw: Fix detecting FIFO depth

Current code tries to find the highest valid fifo depth by checking the value
it wrote to DW_SPI_TXFLTR. There are a few problems in current code:
1) There is an off-by-one in dws->fifo_len setting because it assumes the latest
   register write fails so the latest valid value should be fifo - 1.
2) We know the depth could be from 2 to 256 from HW spec, so it is not necessary
   to test fifo == 257. In the case fifo is 257, it means the latest valid
   setting is fifo = 256. So after the for loop iteration, we should check
   fifo == 2 case instead of fifo == 257 if detecting the FIFO depth fails.
This patch fixes above issues.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-and-tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
index d0d5542efc06..1a0f266c4268 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c
@@ -621,13 +621,13 @@ static void spi_hw_init(struct dw_spi *dws)
         if (!dws->fifo_len) {
                 u32 fifo;
 
-                for (fifo = 2; fifo <= 257; fifo++) {
+                for (fifo = 2; fifo <= 256; fifo++) {
                         dw_writew(dws, DW_SPI_TXFLTR, fifo);
                         if (fifo != dw_readw(dws, DW_SPI_TXFLTR))
                                 break;
                 }
 
-                dws->fifo_len = (fifo == 257) ? 0 : fifo;
+                dws->fifo_len = (fifo == 2) ? 0 : fifo - 1;
                 dw_writew(dws, DW_SPI_TXFLTR, 0);
         }
 }