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SubjectRe: [RESEND PATCH] mips: ralink: allow zboot
Date
Hi George,

On Thu, Mar 21, 2019 at 05:10:38PM -0600, George Hilliard wrote:
> My version of U-Boot complains if I compile out LZMA support:
> ---
> => tftpboot 0x81000000 uImage; tftpboot 0x84000000 hawkeye.dtb; bootm
> 0x81000000 - 0x84000000
> (snip)
> Bytes transferred = 7349 (1cb5 hex)
> ## Booting kernel from Legacy Image at 81000000 ...
> Image Name: Linux-5.1.0-rc1
> Image Type: MIPS Linux Kernel Image (lzma compressed)
> Data Size: 1465871 Bytes = 1.4 MiB
> Load Address: 80000000
> Entry Point: 80344338
> Verifying Checksum ... OK
> ## Flattened Device Tree blob at 84000000
> Booting using the fdt blob at 0x84000000
> Uncompressing Kernel Image ... Unimplemented compression type 3
> exit not allowed from main input shell.
> =>
> ---

There you're using a uImage though, which is different to
CONFIG_SYS_SUPPORTS_ZBOOT. Even without CONFIG_SYS_SUPPORTS_ZBOOT
enabled, you can build either a compressed or uncompressed uImage.

Some platforms enable one of those targets by default but it doesn't
appear that ralink does, so I guess you're specifying a uImage.lzma
target when building the kernel? Try doing that when
CONFIG_SYS_SUPPORTS_ZBOOT isn't enabled - it'll still generate the same
type of LZMA-compressed uImage.

What CONFIG_SYS_SUPPORTS_ZBOOT does is produce a program (vmlinuz) which
contains a compressed version of vmlinux.bin along with some code to
decompress it. The decompression is performed by vmlinuz itself, not by
U-Boot.

A uImage in contrast is just the compressed (or uncompressed)
vmlinux.bin with a header prepended that U-Boot uses to understand what
it's loading. If the header says the data is compressed with LZMA then
U-Boot will need to support LZMA decompression.

What U-Boot is complaining about there is that you gave it a uImage
that's LZMA compressed & your build of U-Boot itself doesn't support
LZMA. That has nothing to do with CONFIG_SYS_SUPPORTS_ZBOOT or whether
the kernel binary itself supports any particular compression algorithm -
it's purely down to the configuration of your copy of U-Boot.

Options would be to rebuild U-Boot with LZMA support enabled, or to use
a different compression for your uImage that U-Boot already supports.
eg. you could specify that you want to use gzip:

$ make ARCH=mips uImage.gz

That would give you an image that will work so long as U-Boot supports
gzip decompression, or:

$ make ARCH=mips uImage.bin

That would give you an uncompressed uImage which U-Boot always supports.

Now it could still be valid to select CONFIG_SYS_SUPPORTS_ZBOOT if you
had a need for a better compression algorithm & couldn't update your
bootloader to support it, but that would be solving a different problem
than your commit message claims & it wouldn't matter at all whether the
bootloader supports a particular compression algorithm.

Thanks,
Paul

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