RE: [RFC] buildtar: add case for riscv architecture

[Anup Patel]

> -----Original Message-----
> From: linux-kernel-owner@xxxxxxxxxxxxxxx <linux-kernel-
> owner@xxxxxxxxxxxxxxx> On Behalf Of Palmer Dabbelt
> Sent: Saturday, September 14, 2019 6:30 PM
> To: mail@xxxxxxxxxxxx
> Cc: Troy Benjegerdes <troy.benjegerdes@xxxxxxxxxx>; Paul Walmsley
> <paul.walmsley@xxxxxxxxxx>; aou@xxxxxxxxxxxxxxxxx; linux-
> riscv@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> kbuild@xxxxxxxxxxxxxxx
> Subject: Re: [RFC] buildtar: add case for riscv architecture
> 
> On Wed, 11 Sep 2019 05:54:07 PDT (-0700), mail@xxxxxxxxxxxx wrote:
> >
> >
> >> None of the available RiscV platforms that Iâm aware of use compressed
> images, unless there are some new bootloaders I havenât seen yet.
> >>
> >
> > I noticed that default build image is Image.gz, which is why I thought its a
> good idea to copy it into the tarball. Does such a copy not make sense at this
> point ?
> 
> Image.gz can't be booted directly: it's just Image that's been compressed
> with the standard gzip command.  A bootloader would have to decompress
> that image before loading it into memory, which requires extra bootloader
> support.
> Contrast that with the zImage style images (which are vmlinuz on x86), which
> are self-extracting and therefor require no bootloader support.  The
> examples for u-boot all use the "booti" command, which expects
> uncompressed images.
> Poking around I couldn't figure out a way to have u-boot decompress the
> images, but that applies to arm64 as well so I'm not sure if I'm missing
> something.
> 
> If I was doing this, I'd copy over arch/riscv/boot/Image and call it
> "/boot/image-${KERNELRELEASE}", as calling it vmlinuz is a bit confusing to
> me because I'd expect vmlinuz to be a self-extracting compressed
> executable and not a raw gzip file.

On the contrary, it is indeed possible to boot Image.gz directly using
U-Boot booti command so this patch would be useful.

Atish had got it working on U-Boot but he has deferred booti Image.gz
support due to few more dependent changes. May be he can share
more info.

Regards,
Anup