From ce99319a182fe766be67f96338386f3ec73e321c 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
Git-commit: ce99319a182fe766be67f96338386f3ec73e321c
Patch-mainline: v4.17-rc1
References: bsc#1051510

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
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/spi/spi.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -775,8 +775,14 @@ static int spi_map_buf(struct spi_master
 	for (i = 0; i < sgs; i++) {
 
 		if (vmalloced_buf || kmap_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)));
 			if (vmalloced_buf)
 				vm_page = vmalloc_to_page(buf);
 			else