[PATCH 3.2 097/221] spi: dw: revisit FIFO size detection again

Ben Hutchings
2015-05-05T01:34:52Z

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

commit 9d239d353c319f9ff884c287ce47feb7cdf60ddc upstream.

The commit d297933cc7fc (spi: dw: Fix detecting FIFO depth) tries to fix the
logic of the FIFO detection based on the description on the comments. However,
there is a slight difference between numbers in TX Level and TX FIFO size.

So, 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.

This patch fixes it eventually right.

Fixes: d297933cc7fc (spi: dw: Fix detecting FIFO depth)
Reviewed-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/spi/spi-dw.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c
@@ -786,13 +786,13 @@ static void spi_hw_init(struct dw_spi *d
*/
if (!dws->fifo_len) {
u32 fifo;
- for (fifo = 2; fifo <= 256; fifo++) {
+ for (fifo = 1; fifo < 256; fifo++) {
dw_writew(dws, DW_SPI_TXFLTR, fifo);
if (fifo != dw_readw(dws, DW_SPI_TXFLTR))
break;
}

- dws->fifo_len = (fifo == 2) ? 0 : fifo - 1;
+ dws->fifo_len = (fifo == 1) ? 0 : fifo;
dw_writew(dws, DW_SPI_TXFLTR, 0);
}
}