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

[Palmer Dabbelt]

On Sat, 14 Sep 2019 06:05:59 PDT (-0700), Anup Patel wrote:
> > -----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.

Oh, great.  I guess it makes sense to just put both in the tarball, then, as 
users will still need to use the Image format for now.

> Regards,
> Anup