ubi: Add "skipcheck" command to set/clear this bit in the UBI volume hdr

U-Boot now supports the "skip_check" flag to optionally skip the CRC
check at open time. Currently its only possible to set this bit upon
UBI volume creation. But it might be very useful to also set this bit
on already installed systems (e.g. field upgrade) to make also use of
the boot-time decrease on those systems.

This patch now adds a new "ubi" command "ubi skipcheck" to set or clear
this bit in the UBI volume header:

=> ubi skipcheck rootfs0 on
Setting skip_check on volume rootfs0

BTW: This saves approx. 10 seconds Linux bootup time on a MT7688 based
target with 128MiB of SPI NAND.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Heiko Schocher <hs@denx.de>
Cc: Quentin Schulz <quentin.schulz@bootlin.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Andreas Dannenberg <dannenberg@ti.com>

cmd/ubi.c

@@ -419,6 +419,30 @@ static int ubi_dev_scan(struct mtd_info *info, const char *vid_header_offset)
 	return 0;
 }
 
+static int ubi_set_skip_check(char *volume, bool skip_check)
+{
+	struct ubi_vtbl_record vtbl_rec;
+	struct ubi_volume *vol;
+
+	vol = ubi_find_volume(volume);
+	if (!vol)
+		return ENODEV;
+
+	printf("%sing skip_check on volume %s\n",
+	       skip_check ? "Sett" : "Clear", volume);
+
+	vtbl_rec = ubi->vtbl[vol->vol_id];
+	if (skip_check) {
+		vtbl_rec.flags |= UBI_VTBL_SKIP_CRC_CHECK_FLG;
+		vol->skip_check = 1;
+	} else {
+		vtbl_rec.flags &= ~UBI_VTBL_SKIP_CRC_CHECK_FLG;
+		vol->skip_check = 0;
+	}
+
+	return ubi_change_vtbl_record(ubi, vol->vol_id, &vtbl_rec);
+}
+
 static int ubi_detach(void)
 {
 #ifdef CONFIG_CMD_UBIFS
@@ -578,6 +602,14 @@ static int do_ubi(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 			return ubi_remove_vol(argv[2]);
 	}
 
+	if (strncmp(argv[1], "skipcheck", 9) == 0) {
+		/* E.g., change skip_check flag */
+		if (argc == 4) {
+			skipcheck = strncmp(argv[3], "on", 2) == 0;
+			return ubi_set_skip_check(argv[2], skipcheck);
+		}
+	}
+
 	if (strncmp(argv[1], "write", 5) == 0) {
 		int ret;
 
@@ -658,6 +690,7 @@ U_BOOT_CMD(
 		" - Read volume to address with size\n"
 	"ubi remove[vol] volume"
 		" - Remove volume\n"
+	"ubi skipcheck volume on/off - Set or clear skip_check flag in volume header\n"
 	"[Legends]\n"
 	" volume: character name\n"
 	" size: specified in bytes\n"

doc/README.ubi

@@ -223,3 +223,36 @@ For example:
 
 => ubifsumount
 Unmounting UBIFS volume recovery!
+
+
+Usage of the UBI CRC skip-check flag of static volumes:
+-------------------------------------------------------
+Some users of static UBI volumes implement their own integrity check,
+thus making the volume CRC check done at open time useless. For
+instance, this is the case when one use the ubiblock + dm-verity +
+squashfs combination, where dm-verity already checks integrity of the
+block device but this time at the block granularity instead of verifying
+the whole volume.
+
+Skipping this test drastically improves the boot-time.
+
+U-Boot now supports the "skip_check" flag to optionally skip the CRC
+check at open time.
+
+Usage: Case A - Upon UBI volume creation:
+You can optionally add "--skipcheck" to the "ubi create" command:
+
+ubi create[vol] volume [size] [type] [id] [--skipcheck]
+ - create volume name with size ('-' for maximum available size)
+
+Usage: Case B - With an already existing UBI volume:
+Use the "ubi skipcheck" command:
+
+ubi skipcheck volume on/off - Set or clear skip_check flag in volume header
+
+Example:
+=> ubi skipcheck rootfs0 on
+Setting skip_check on volume rootfs0
+
+BTW: This saves approx. 10 seconds Linux bootup time on a MT7688 based
+target with 128MiB of SPI NAND.