[PATCH] dfu: mtd: skip empty pages when writing page for UBI partition

[Patrick Delaunay]

Align the DFU MTD backend for the UBI partitions with the mtd command write
behavior when the option .dontskipff is not used: don't write the empty
pages (full of 0xFF); it is not required for UBI, see [1] for details.

This patch avoids the "free space fixup" procedure in the kernel [2]
and allows to program a UBIFS volume generated by mkfs.ubifs without the
option -F, --space-fixup.

The MTD DFU backend implements this behavior introduced on DFU NAND
backend by the commit 13cb7cc9e8e4 ("dfu: Add option to skip empty pages
when flashing UBI images to NAND") and also supported by the command nand
by CONFIG_CMD_NAND_TRIMFFS and by commit c9494866df83 ("cmd_nand: add nand
write.trimffs command").

[1] http://www.linux-mtd.infradead.org/doc/ubi.html#L_flasher_algo
[2] http://www.linux-mtd.infradead.org/faq/ubifs.html#L_free_space_fixup

Signed-off-by: Patrick Delaunay <patrick.delaunay at foss.st.com>
---

 drivers/dfu/dfu_mtd.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/dfu/dfu_mtd.c b/drivers/dfu/dfu_mtd.c
index 0b7f17761f..cce9ce0845 100644
--- a/drivers/dfu/dfu_mtd.c
+++ b/drivers/dfu/dfu_mtd.c
@@ -18,6 +18,20 @@ static bool mtd_is_aligned_with_block_size(struct mtd_info *mtd, u64 size)
 	return !do_div(size, mtd->erasesize);
 }
 
+/* Logic taken from cmd/mtd.c:mtd_oob_write_is_empty() */
+static bool mtd_page_is_empty(struct mtd_oob_ops *op)
+{
+	int i;
+
+	for (i = 0; i < op->len; i++)
+		if (op->datbuf[i] != 0xff)
+			return false;
+
+	/* oob is not used, with MTD_OPS_AUTO_OOB & ooblen=0 */
+
+	return true;
+}
+
 static int mtd_block_op(enum dfu_op op, struct dfu_entity *dfu,
 			u64 offset, void *buf, long *len)
 {
@@ -129,8 +143,14 @@ static int mtd_block_op(enum dfu_op op, struct dfu_entity *dfu,
 
 		if (op == DFU_OP_READ)
 			ret = mtd_read_oob(mtd, off, &io_op);
-		else
+		else if (has_pages && dfu->data.mtd.ubi && mtd_page_is_empty(&io_op)) {
+			/* in case of ubi partition, do not write an empty page, only skip it */
+			ret = 0;
+			io_op.retlen = mtd->writesize;
+			io_op.oobretlen = mtd->oobsize;
+		} else {
 			ret = mtd_write_oob(mtd, off, &io_op);
+		}
 
 		if (ret) {
 			printf("Failure while %s at offset 0x%llx\n",
-- 
2.25.1