spi: designware_spi: revisit FIFO size detection again

By specification the FIFO size would be in a range 2-256 bytes. From TX Level
prospective it means we can set threshold in the range 0-(FIFO size - 1) bytes.
Hence there are currently two issues:
  a) FIFO size 2 bytes is actually skipped since TX Level is 1 bit and could be
     either 0 or 1 byte;
  b) FIFO size is incorrectly decreased by 1 which already done by meaning of
     TX Level register.

Fixes: 501943696ea4 (spi: designware_spi: Fix detecting FIFO depth)
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Pavel Machek <pavel@denx.de>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>

diff --git a/drivers/spi/designware_spi.c b/drivers/spi/designware_spi.c
index 2624844d528566bb7ed786ae06537b4cbf69b777..8f5c0fc8029d6b862bbbf1962ae55a27d80ec531 100644 (file)
--- a/drivers/spi/designware_spi.c
+++ b/drivers/spi/designware_spi.c
@@ -164,13 +164,13 @@ static void spi_hw_init(struct dw_spi_priv *priv)
        if (!priv->fifo_len) {
                u32 fifo;
 
-               for (fifo = 2; fifo <= 256; fifo++) {
+               for (fifo = 1; fifo < 256; fifo++) {
                        dw_writew(priv, DW_SPI_TXFLTR, fifo);
                        if (fifo != dw_readw(priv, DW_SPI_TXFLTR))
                                break;
                }
 
-               priv->fifo_len = (fifo == 2) ? 0 : fifo - 1;
+               priv->fifo_len = (fifo == 1) ? 0 : fifo;
                dw_writew(priv, DW_SPI_TXFLTR, 0);
        }
        debug("%s: fifo_len=%d\n", __func__, priv->fifo_len);