mtd: spi-nor: add read loop

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=26f9bcad29a6c240881bd4efc90f16a9990dd6c2
Commit:     26f9bcad29a6c240881bd4efc90f16a9990dd6c2
Parent:     e5d05cbd6d8b01f08c95c427a36c66aac769af4f
Author:     Michal Suchanek <hramrach at gmail.com>
AuthorDate: Thu May 5 17:31:55 2016 -0700
Committer:  Brian Norris <computersforpeace at gmail.com>
CommitDate: Wed Jun 1 17:23:02 2016 -0700

    mtd: spi-nor: add read loop
    
    mtdblock and ubi do not handle the situation when read returns less data
    than requested. Loop in spi-nor until buffer is filled or an error is
    returned.
    
    Signed-off-by: Michal Suchanek <hramrach at gmail.com>
    Signed-off-by: Brian Norris <computersforpeace at gmail.com>
    Tested-by Cyrille Pitchen <cyrille.pitchen at atmel.com>
    Acked-by: Michal Suchanek <hramrach at gmail.com>
    Tested-by: Michal Suchanek <hramrach at gmail.com>
---
 drivers/mtd/spi-nor/spi-nor.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index fe55b48..a63922e 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1031,14 +1031,27 @@ static int spi_nor_read(struct mtd_info *mtd, loff_t from, size_t len,
 	if (ret)
 		return ret;
 
-	ret = nor->read(nor, from, len, buf);
+	while (len) {
+		ret = nor->read(nor, from, len, buf);
+		if (ret == 0) {
+			/* We shouldn't see 0-length reads */
+			ret = -EIO;
+			goto read_err;
+		}
+		if (ret < 0)
+			goto read_err;
 
-	spi_nor_unlock_and_unprep(nor, SPI_NOR_OPS_READ);
-	if (ret < 0)
-		return ret;
+		WARN_ON(ret > len);
+		*retlen += ret;
+		buf += ret;
+		from += ret;
+		len -= ret;
+	}
+	ret = 0;
 
-	*retlen += ret;
-	return 0;
+read_err:
+	spi_nor_unlock_and_unprep(nor, SPI_NOR_OPS_READ);
+	return ret;
 }
 
 static int sst_write(struct mtd_info *mtd, loff_t to, size_t len,