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.fala...@keymile.com>
Cc: Valentin Longchamp <valentin.longch...@keymile.com>
Cc: Holger Brunck <holger.bru...@keymile.com>
---
 common/cmd_sf.c |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/common/cmd_sf.c b/common/cmd_sf.c
index d97d4a5..0666f52 100644
--- a/common/cmd_sf.c
+++ b/common/cmd_sf.c
@@ -134,8 +134,10 @@ 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);
@@ -145,6 +147,17 @@ 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;
-- 
1.7.1

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