dfu: Add option to skip empty pages when flashing UBI images to NAND

Add a new option to enable the DROP_FFS flag when flashing UBI images to
NAND in order to drop trailing all-0xff pages.

This is similar to the existing FASTBOOT_FLASH_NAND_TRIMFFS option.
Signed-off-by: NGuillermo Rodriguez <guille.rodriguez@gmail.com>
Cc: Lukasz Majewski <lukma@denx.de>

drivers/dfu/Kconfig

@@ -42,6 +42,13 @@ config DFU_NAND
 	  This option enables using DFU to read and write to NAND based
 	  storage.
 
+config DFU_NAND_TRIMFFS
+	bool "Skip empty pages when flashing UBI images to NAND"
+	depends on DFU_NAND
+	help
+	  When flashing UBI images to NAND, enable the DROP_FFS flag to drop
+	  trailing all-0xff pages.
+
 config DFU_RAM
 	bool "RAM back end for DFU"
 	help

drivers/dfu/dfu_nand.c

@@ -50,6 +50,7 @@ static int nand_block_op(enum dfu_op op, struct dfu_entity *dfu,
 					 lim, buf);
 	} else {
 		nand_erase_options_t opts;
+		int write_flags = WITH_WR_VERIFY;
 
 		memset(&opts, 0, sizeof(opts));
 		opts.offset = start;
@@ -62,8 +63,12 @@ static int nand_block_op(enum dfu_op op, struct dfu_entity *dfu,
 		if (ret)
 			return ret;
 		/* then write */
+#ifdef CONFIG_DFU_NAND_TRIMFFS
+		if (dfu->data.nand.ubi)
+			write_flags |= WITH_DROP_FFS;
+#endif
 		ret = nand_write_skip_bad(mtd, start, &count, &actual,
-					  lim, buf, WITH_WR_VERIFY);
+					  lim, buf, write_flags);
 	}
 
 	if (ret != 0) {