spi: designware_spi: 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>
Acked-by: Stefan Roese <sr@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 98c9f03..0210667 100644
--- a/drivers/spi/designware_spi.c
+++ b/drivers/spi/designware_spi.c
@@ -164,13 +164,13 @@
if (!priv->fifo_len) {
u32 fifo;
- for (fifo = 2; fifo <= 257; fifo++) {
+ for (fifo = 2; fifo <= 256; fifo++) {
dw_writew(priv, DW_SPI_TXFLTR, fifo);
if (fifo != dw_readw(priv, DW_SPI_TXFLTR))
break;
}
- priv->fifo_len = (fifo == 257) ? 0 : fifo;
+ priv->fifo_len = (fifo == 2) ? 0 : fifo - 1;
dw_writew(priv, DW_SPI_TXFLTR, 0);
}
debug("%s: fifo_len=%d\n", __func__, priv->fifo_len);