[OpenWrt-Devel] [PATCH 2/2] ramips: mt7621: use lzma-loader for D-Link DIR-860L

[Chuanhong Guo]

Hi!

On Sun, Apr 19, 2020 at 8:38 AM Szabolcs Hubai <szab.hu at gmail.com> wrote:
>
> This device has trouble extracting big kernel from flash,
> and supports LZMA compressed kernels only.
>
> Using OpenWrt kernel loader saves us 64 KB compared to the dictionary
> size limiting workaround.
>
> Factory image sizes (commit: 5f126c541a74) with "CONFIG_ALL_KMODS=y":
> - original ("-d23", default): 4784188 bytes, LZMA ERROR 1
> - with "-d19": 4915260, LZMA ERROR 1
> - with "-d18": 4915260, diff to original: +128 KB
> - with "-d17": 4980796, diff to original: +192 KB
> - with this patch: 4849724, diff to original: +64 KB
>
> To save some CPU cycle, use minimal compression ("-a0") for the LZMA
> compressed uImage.

My original thought on this device is to use a different loader. The first
4MB of SPI-NOR flash on mt7621 is mapped to 0x1fc00000 and lzma
loader can read compressed kernel directly from flash. If the kernel
can be put at a fixed offset in flash, we could compress lzma loader
separately and let u-boot decompress only the loader.
You could take a look at the tp-link-nolzma recipe in:
target/linux/ath79/image/common-tp-link.mk
and see if you could implement a similar solution for mt7621.
Note: You need to fix AR71XX_FLASH_START defined in:
target/linux/ramips/image/lzma-loader/src/loader.c
to 0x1fc00000 for this method to work.

If you can't implement it, I'm fine with your current solution too.
but I prefer to drop patch 1/2 and write the complete kernel
recipe for dir-860l only. It's a bit confusing to use "KERNEL +="

-- 
Regards,
Chuanhong Guo

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