[3.16.y-ckt stable] Patch "spi: dw: revisit FIFO size detection again" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Tue Mar 24 15:33:59 UTC 2015

This is a note to let you know that I have just added a patch titled

    spi: dw: revisit FIFO size detection again

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:


This patch is scheduled to be released in version 3.16.7-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see



>From e44ea338a814f89f86dc3243a2915d6a4f786937 Mon Sep 17 00:00:00 2001
From: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
Date: Wed, 25 Feb 2015 11:39:36 +0200
Subject: spi: dw: revisit FIFO size detection again

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 at ingics.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
Signed-off-by: Mark Brown <broonie at kernel.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.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 32a3718cc5b4..4fc4c20893e1 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c
@@ -622,13 +622,13 @@ 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))

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

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