image: improve UBI image sizing on NAND devices

Many NAND devices use a build recipe with "append-ubi | check-size" to
ensure factory images don't exceed the target flash partition size.
However, UBI reserves space for bad block handling and other operational
overhead, and thus 'check-size' can overestimate the space available by
several MB. In practice, this means a failed check is definitely a failure,
while a passing check is only probably a pass.

Improve the situation by teaching 'Build/append-ubi' to check image sizes
while accounting for UBI reserved blocks. Add new device variable NAND_SIZE
and use with existing IMAGE_SIZE to derate the available space. Each UBI
device reserves 20 PEBs per 1024 PEBs of the entire NAND device for bad
blocks, plus an additional 4 PEBs overhead.

Many devices can transparently enable this check by setting NAND_SIZE based
on their flash storage, and may then remove any unneeded 'check-size'.

Link: http://www.linux-mtd.infradead.org/doc/ubi.html#L_overhead

Suggested-by: Shiji Yang <[email protected]>
Suggested-by: Robert Marko <[email protected]>
Signed-off-by: Tony Ambardar <[email protected]>

include/image-commands.mk

@@ -133,6 +133,8 @@ define Build/append-md5sum-ascii-salted
 	rm [email protected]
 endef
 
+UBI_NAND_SIZE_LIMIT = $(IMAGE_SIZE) - ($(NAND_SIZE)*20/1024 + 4*$(BLOCKSIZE))
+
 define Build/append-ubi
 	sh $(TOPDIR)/scripts/ubinize-image.sh \
 		$(if $(UBOOTENV_IN_UBI),--uboot-env) \
@@ -146,6 +148,8 @@ define Build/append-ubi
 		$(UBINIZE_OPTS)
 	cat [email protected] >> $@
 	rm [email protected]
+	$(if $(and $(IMAGE_SIZE),$(NAND_SIZE)),\
+		$(call Build/check-size,$(UBI_NAND_SIZE_LIMIT)))
 endef
 
 define Build/ubinize-kernel

include/image.mk

@@ -397,6 +397,7 @@ define Device/Init
   DEVICE_IMG_NAME = $$(DEVICE_IMG_PREFIX)-$$(1)-$$(2)
   FACTORY_IMG_NAME :=
   IMAGE_SIZE :=
+  NAND_SIZE :=
   KERNEL_PREFIX = $$(DEVICE_IMG_PREFIX)
   KERNEL_SUFFIX := -kernel.bin
   KERNEL_INITRAMFS_SUFFIX = $$(KERNEL_SUFFIX)
@@ -457,7 +458,7 @@ DEFAULT_DEVICE_VARS := \
   DEVICE_DTS_DIR DEVICE_DTS_OVERLAY DEVICE_DTS_LOADADDR \
   DEVICE_FDT_NUM DEVICE_IMG_PREFIX SOC BOARD_NAME UIMAGE_MAGIC UIMAGE_NAME \
   UIMAGE_TIME SUPPORTED_DEVICES IMAGE_METADATA KERNEL_ENTRY KERNEL_LOADADDR \
-  UBOOT_PATH IMAGE_SIZE \
+  UBOOT_PATH IMAGE_SIZE NAND_SIZE \
   FACTORY_IMG_NAME FACTORY_SIZE \
   DEVICE_PACKAGES DEVICE_COMPAT_VERSION DEVICE_COMPAT_MESSAGE \
   DEVICE_VENDOR DEVICE_MODEL DEVICE_VARIANT \