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.

---
 drivers/spi/spi-dw.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index d0d5542..1a0f266 100644
@@ -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);
 	}
 }

1.9.1



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Applied, thanks.