Re: [PATCH v2 0/2] ARM: decompressor: support AUTO_ZRELADDR and appended DTB

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Wed, Feb 04, 2026 at 11:53:30AM +0100, Geert Uytterhoeven wrote:
> Hi Russell,
> 
> On Wed, 4 Feb 2026 at 02:27, Russell King (Oracle)
> <linux@armlinux.org.uk> wrote:
> > On Wed, Feb 04, 2026 at 01:36:29AM +0100, Linus Walleij wrote:
> > > However, I think it is a thick requirement to put on hobbyist
> > > contributors to go and write entite boot loaders from scratch,
> > > I think it's a fine requirement to put on Qualcomm or Renesas
> > > paid maintainers.
> >
> > If we're talking about older boards, then why have they only recently
> > became a problem, when, presumably, they've been working fine for a
> > decade or so?
> 
> These boards may have been working fine, given the right "legacy"
> kernel config options were used.  However, some of these option make
> the resulting kernel limited to that platform or even to a specific
> board (e.g. when CONFIG_CMDLINE needs to be used).

The 32-git ARM kernel has had a way to pass the command line to the
kernel from the boot loader since day one.

	First it was the struct param_struct.
	Then it was the ATAGs that was introduced pre-git.
	Now it is DT.

The kernel retains code to parse all three methods of passing data
from the boot loader to the kernel. The decompressor has support
for merging the ATAGs into the appended DTB, which includes merging
the command line into the DTB.

Without an appended DTB, the pointer to one of the above will be
passed to the kernel, the kernel will figure out what it has and
parse one of the three ways, and use the command line there.

The only case where CONFIG_CMDLINE should be used is when there is
no command line passed, no way to change it, etc. At that point
there are two options:

1. Augment the kernel's generated FDT with the command line node
   and load that modified FDT or append it to the compressed image.

2. Use CONFIG_CMDLINE, which means that the kernel _will_ become
   specific to the platform that needs those arguments. No getting
   away from that in this case.

Maybe you haven't explained the problem very well, but I don't see
any issue with this.

> The KZM-A9-GT I "need" this for never had upstream U-Boot (I don't
> think I ever had any U-Boot sources).  I can boot a shmobile_defconfig
> multi-platform kernel[*] fine, iff the first patch is applied.

So, what have you been doing for the last 14 years to boot this
platform (merged in 2012) without this patch?

Please explain:

- how it worked before - I want to know how the DTB is passed to the
  kernel, what information is provided from the boot loader, whether
  that gets merged into the DTB, etc. All the fine nitty gritty of
  how it worked and what doesn't work, what the problems were etc.

- what changed (it sounds like you want extra features)

- why (in detail) it doesn't work now.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!