[PATCH v2] mtd: m25p80: consider max message size in m25p80_read

[Heiner Kallweit <hkallweit1-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Consider a message size limit when calculating the maximum amount
of data that can be read.

The message size limit has been introduced with 4.9, so cc it
to stable.

Signed-off-by: Heiner Kallweit <hkallweit1-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: <stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org> # 4.9.x
---
v2:
- This patch was part of a series and the other patches of the
  series went into 4.9. It's needed to correctly support
  reads > 64k on fsl-espi as first user of spi_max_message_size.
  See commit 02a595d5d6e4 ("spi: fsl-espi: eliminate spi nor
  flash read loop"). CC it to stable.  
---
 drivers/mtd/devices/m25p80.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
index 9cf7fcd..16a7df2 100644
--- a/drivers/mtd/devices/m25p80.c
+++ b/drivers/mtd/devices/m25p80.c
@@ -172,7 +172,8 @@ static ssize_t m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
 
 	t[1].rx_buf = buf;
 	t[1].rx_nbits = m25p80_rx_nbits(nor);
-	t[1].len = min(len, spi_max_transfer_size(spi));
+	t[1].len = min3(len, spi_max_transfer_size(spi),
+			spi_max_message_size(spi) - t[0].len);
 	spi_message_add_tail(&t[1], &m);
 
 	ret = spi_sync(spi, &m);
-- 
2.9.2


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