[PATCH] ARM: Fix support for CMDLINE_EXTEND

[Maxim Uvarov]

It will be good  to have some constance here with other arches:
./arch/arm/kernel/atags_parse.c:#if defined(CONFIG_CMDLINE_EXTEND)
./arch/sh/kernel/setup.c:#ifdef CONFIG_CMDLINE_EXTEND
./arch/powerpc/kernel/prom_init.c:    if
(IS_ENABLED(CONFIG_CMDLINE_EXTEND) || l <= 0 || p[0] == '\0')
./arch/loongarch/kernel/setup.c:     * CONFIG_CMDLINE_EXTEND is enabled.
./arch/loongarch/kernel/setup.c:    if
(IS_ENABLED(CONFIG_CMDLINE_EXTEND) && CONFIG_CMDLINE[0]) {
./arch/riscv/kernel/pi/cmdline_early.c:    if
(IS_ENABLED(CONFIG_CMDLINE_EXTEND) ||

Or drop CONFIG_CMDLINE_EXTEND completely or make arm64 work as others.

BR,
Maxim.

пн, 31 мар. 2025 г. в 16:35, Russell King (Oracle) <linux at armlinux.org.uk>:
>
> On Mon, Mar 31, 2025 at 01:55:23PM +0100, Russell King (Oracle) wrote:
> > On Mon, Mar 31, 2025 at 08:29:21AM +0000, 谢致邦 (XIE Zhibang) wrote:
> > > > Later arguments override earlier arguments. Any compiled-in command line
> > > > needs to be overridable by user supplied input from the boot loader. The
> > > > current behaviour is correct.
> > >
> > > CMDLINE_EXTEND is for the built-in command line to "Extend bootloader kernel
> > > arguments", not for the bootloader command line to extend/override built-in
> > > command line.
> > >
> > > Don't forget that the default empty CMDLINE already gives the bootloader the
> > > ability to override everything. Not to mention that even if CMDLINE is not
> > > empty, the default CMDLINE_FROM_BOOTLOADER continues to give the bootloader the
> > > ability to override all.
> >
> > The help text:
> >
> > +         The command-line arguments provided by the boot loader will be
> > +         appended to the default kernel command string.
> >
> > so, you end up with default kernel command string _followed by_ the
> > boot loader arguments. This allows the boot loader arguments to
> > override anything that is in the default kernel command string.
> > That's why it is a _default_ - it can be overrided.
> >
> > If the boot loader command string is extended by the default kernel
> > command string, then that doesn't happen.
> >
> > CMDLINE_EXTEND is default _followed by_ boot loader.
> >
> > You're wanting it to be the other way around. That's broken.
>
> To add further weight:
>
> ARM gained support for CMDLINE_EXTEND in commit 4394c1244249 ("ARM:
> 6893/1: Allow for kernel command line concatenation") dated 4 May
> 2011. In this commit, CONFIG_CMDLINE _prefixes_ the boot loader
> supplied arguments.
>
> In commit 34b82026a507 ("fdt: fix extend of cmd line") dated 13
> April 2016, which _post_ _dates_ the introduction on ARM, and the
> commit even states that it's fixing the lack of appending compared
> to ARM, this adds code to drivers/of to _append_ CONFIG_CMDLINE
> to the FDT arguments which come from the boot loader.
>
> It is DT that implemented this wrongly.
>
> No, we are not going to change arch/arm to conform to something
> that was implemented in a broken way. drivers/of needs fixing
> to actually implement it as it was *originally* intended - and
> there is five years of arch/arm doing this *before* DT started
> to do it.
>
> If drivers/of maintainers also don't want to change, then I'm
> sorry, but you have to then put up with the fact that it got
> wrongly implemented by drivers/of and thus has a different
> behaviour there.
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!



-- 
Best regards,
Maxim Uvarov