ath79: optimize the firmware recipe for Netgear NAND devices

1. Drop useless character '0xff' before fake filesystem header.
2. Reduce useless padding to shrink the size of the sysupgrade image.
3. Do not check the size of sysupgrade image. It does not make sense to
   check the size of a compressed package.
4. Do not take the size of netgear header into account because it will
   not be written to Flash.
5. Use the default lzma compression dictionary parameter '-d24' to get
   better performance.

Tested on Netgear R6100
Signed-off-by: Shiji Yang <[email protected]>

target/linux/ath79/image/nand.mk

@@ -230,7 +230,7 @@ define Device/linksys_ea4500-v3
 endef
 TARGET_DEVICES += linksys_ea4500-v3
 
-# fake rootfs is mandatory, pad-offset 129 equals (2 * uimage_header + 0xff)
+# fake rootfs is mandatory, pad-offset 64 equals (1 * uimage_header)
 define Device/netgear_ath79_nand
   DEVICE_VENDOR := NETGEAR
   DEVICE_PACKAGES := kmod-usb2 kmod-usb-ledtrig-usbport
@@ -238,15 +238,12 @@ define Device/netgear_ath79_nand
   BLOCKSIZE := 128k
   PAGESIZE := 2048
   IMAGE_SIZE := 25600k
-  KERNEL := kernel-bin | append-dtb | lzma -d20 | \
-	pad-offset $$(KERNEL_SIZE) 129 | uImage lzma | \
-	append-string -e '\xff' | \
-	append-uImage-fakehdr filesystem $$(UIMAGE_MAGIC)
-  KERNEL_INITRAMFS := kernel-bin | append-dtb | lzma -d20 | uImage lzma
+  KERNEL := kernel-bin | append-dtb | lzma | uImage lzma | \
+	pad-offset $$(BLOCKSIZE) 64 | append-uImage-fakehdr filesystem $$(UIMAGE_MAGIC)
   IMAGES := sysupgrade.bin factory.img
-  IMAGE/factory.img := append-kernel | append-ubi | netgear-dni | \
-	check-size
-  IMAGE/sysupgrade.bin := sysupgrade-tar | check-size | append-metadata
+  IMAGE/factory.img := append-kernel | pad-to $$$$(KERNEL_SIZE) | \
+	append-ubi | check-size | netgear-dni
+  IMAGE/sysupgrade.bin := sysupgrade-tar | append-metadata
   UBINIZE_OPTS := -E 5
 endef
 
@@ -262,8 +259,7 @@ define Device/netgear_pgzng1
   IMAGE_SIZE := 83968k
   PAGESIZE := 2048
   BLOCKSIZE := 128k
-  KERNEL := kernel-bin | append-dtb | lzma | uImage lzma
-  IMAGE/sysupgrade.bin := sysupgrade-tar | check-size | append-metadata
+  IMAGE/sysupgrade.bin := sysupgrade-tar | append-metadata
 endef
 TARGET_DEVICES += netgear_pgzng1