linux-kernel - RE: [RFC] buildtar: add case for riscv architecture

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Date:   Sat, 14 Sep 2019 12:27:44 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     Anup Patel <Anup.Patel@....com>
CC:     mail@...abindo.in, Troy Benjegerdes <troy.benjegerdes@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject:     RE: [RFC] buildtar: add case for riscv architecture

On Sat, 14 Sep 2019 06:05:59 PDT (-0700), Anup Patel wrote:
> 
> 
>> -----Original Message-----
>> From: linux-kernel-owner@...r.kernel.org <linux-kernel-
>> owner@...r.kernel.org> On Behalf Of Palmer Dabbelt
>> Sent: Saturday, September 14, 2019 6:30 PM
>> To: mail@...abindo.in
>> Cc: Troy Benjegerdes <troy.benjegerdes@...ive.com>; Paul Walmsley
>> <paul.walmsley@...ive.com>; aou@...s.berkeley.edu; linux-
>> riscv@...ts.infradead.org; linux-kernel@...r.kernel.org; linux-
>> kbuild@...r.kernel.org
>> Subject: Re: [RFC] buildtar: add case for riscv architecture
>> 
>> On Wed, 11 Sep 2019 05:54:07 PDT (-0700), mail@...abindo.in wrote:
>> >
>> >
>> >> None of the available RiscV platforms that I’m aware of use compressed
>> images, unless there are some new bootloaders I haven’t 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