Re: FAILED: patch "[PATCH] spi: Fix scatterlist elements size in spi_map_buf" failed to apply to 4.4-stable tree

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

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Hi Greg,

On Thu, Apr 19, 2018 at 06:22:16PM +0200, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 4.4-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

The attached backported patch should apply to v4.4-stable.

--
Regards
Sudip

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>From b9667cbde9b1934de1fed3a45ee3266f140cf0ec Mon Sep 17 00:00:00 2001
From: Maxime Chevallier <maxime.chevallier@bootlin.com>
Date: Fri, 2 Mar 2018 15:55:09 +0100
Subject: [PATCH] spi: Fix scatterlist elements size in spi_map_buf

commit ce99319a182fe766be67f96338386f3ec73e321c upstream

When SPI transfers can be offloaded using DMA, the SPI core need to
build a scatterlist to make sure that the buffer to be transferred is
dma-able.

This patch fixes the scatterlist entry size computation in the case
where the maximum acceptable scatterlist entry supported by the DMA
controller is less than PAGE_SIZE, when the buffer is vmalloced.

For each entry, the actual size is given by the minimum between the
desc_len (which is the max buffer size supported by the DMA controller)
and the remaining buffer length until we cross a page boundary.

Fixes: 65598c13fd66 ("spi: Fix per-page mapping of unaligned vmalloc-ed buffer")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
---
 drivers/spi/spi.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index dee1cb87d24f..04fd651f9e3e 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -707,8 +707,14 @@ static int spi_map_buf(struct spi_master *master, struct device *dev,
 	for (i = 0; i < sgs; i++) {
 
 		if (vmalloced_buf) {
-			min = min_t(size_t,
-				    len, desc_len - offset_in_page(buf));
+			/*
+			 * Next scatterlist entry size is the minimum between
+			 * the desc_len and the remaining buffer length that
+			 * fits in a page.
+			 */
+			min = min_t(size_t, desc_len,
+				    min_t(size_t, len,
+					  PAGE_SIZE - offset_in_page(buf)));
 			vm_page = vmalloc_to_page(buf);
 			if (!vm_page) {
 				sg_free_table(sgt);
-- 
2.11.0