linux-kernel - [PATCH 3.2 080/152] spi: dw: Fix detecting FIFO depth

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Message-ID: <lsq.1424137613.853950692@decadent.org.uk>
Date:	Tue, 17 Feb 2015 01:46:53 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Axel Lin" <axel.lin@...ics.com>,
	"Mark Brown" <broonie@...nel.org>
Subject: [PATCH 3.2 080/152] spi: dw: Fix detecting FIFO depth

3.2.67-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Axel Lin <axel.lin@...ics.com>

commit d297933cc7fcfbaaf2d37570baac73287bf0357d upstream.

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@...ics.com>
Reviewed-and-tested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Signed-off-by: Mark Brown <broonie@...nel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.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 <= 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);
 	}
 }

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