[U-Boot] [PATCH v2 2/2] cmd_sf: "sf update" preserve the final part of the last sector

[Gerlando Falauto <gerlando.falauto@keymile.com>]

Since "sf update" erases the last block as a whole, but only rewrites
the meaningful initial part of it, the rest would be left erased,
potentially erasing meaningful information.
So, as a safety measure, have it rewrite the original content.

Signed-off-by: Gerlando Falauto <gerlando.falauto@keymile.com>
Cc: Valentin Longchamp <valentin.longchamp@keymile.com>
Cc: Holger Brunck <holger.brunck@keymile.com>
Acked-by: Simon Glass <sjg@chromium.org>
---
 common/cmd_sf.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/common/cmd_sf.c b/common/cmd_sf.c
index ab35a94..fb87d24 100644
--- a/common/cmd_sf.c
+++ b/common/cmd_sf.c
@@ -152,8 +152,10 @@ static const char *spi_flash_update_block(struct spi_flash *flash, u32 offset,
 {
 	debug("offset=%#x, sector_size=%#x, len=%#zx\n",
 		offset, flash->sector_size, len);
-	if (spi_flash_read(flash, offset, len, cmp_buf))
+	/* Read the entire sector so to allow for rewriting */
+	if (spi_flash_read(flash, offset, flash->sector_size, cmp_buf))
 		return "read";
+	/* Compare only what is meningful (len) */
 	if (memcmp(cmp_buf, buf, len) == 0) {
 		debug("Skip region %x size %zx: no change\n",
 			offset, len);
@@ -163,6 +165,17 @@ static const char *spi_flash_update_block(struct spi_flash *flash, u32 offset,
 	/* Erase the entire sector */
 	if (spi_flash_erase(flash, offset, flash->sector_size))
 		return "erase";
+	/* If it's a partial sector, preserve the existing part */
+	if (len != flash->sector_size) {
+		/* Overwrite the first part of the sector with input data */
+		memcpy(cmp_buf, buf, len);
+		/* Rewrite the whole sector with original data at the end */
+		if (spi_flash_write(flash, offset, flash->sector_size,
+					cmp_buf))
+			return "write";
+		return NULL;
+	}
+	/* Rewrite the whole block from the source */
 	if (spi_flash_write(flash, offset, len, buf))
 		return "write";
 	return NULL;
-- 
1.7.10.1