linux-kernel - [PATCH 3.4 173/176] spi: dw: revisit FIFO size detection again

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Message-Id: <1428569224-23820-173-git-send-email-lizf@kernel.org>
Date:	Thu,  9 Apr 2015 16:47:01 +0800
From:	lizf@...nel.org
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Mark Brown <broonie@...nel.org>, Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 173/176] spi: dw: revisit FIFO size detection again

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

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

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


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@...ics.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Signed-off-by: Mark Brown <broonie@...nel.org>
Signed-off-by: Zefan Li <lizefan@...wei.com>
---
 drivers/spi/spi-dw.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
index 71ef1e4..cce2d7b 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c
@@ -780,13 +780,13 @@ static void spi_hw_init(struct dw_spi *dws)
 	 */
 	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);
 	}
 }
-- 
1.9.1

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