linux-kernel - Re: [PATCH v3 05/17] arm: Convert to GENERIC

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Date:   Fri, 26 Mar 2021 12:22:04 -0600
From:   Rob Herring <robh@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Nicolas Pitre <nico@...xnic.net>
Cc:     Will Deacon <will@...nel.org>, Daniel Walker <danielwa@...co.com>,
        Daniel Gimpelevich <daniel@...pelevich.san-francisco.ca.us>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>, devicetree@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        microblaze <monstr@...str.eu>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        nios2 <ley.foon.tan@...el.com>,
        Openrisc <openrisc@...ts.librecores.org>,
        linux-hexagon@...r.kernel.org,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        X86 ML <x86@...nel.org>, linux-xtensa@...ux-xtensa.org,
        SH-Linux <linux-sh@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>
Subject: Re: [PATCH v3 05/17] arm: Convert to GENERIC_CMDLINE

+Nico who added the line in question.

On Fri, Mar 26, 2021 at 9:50 AM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
>
>
> Le 26/03/2021 à 16:47, Rob Herring a écrit :
> > On Fri, Mar 26, 2021 at 7:44 AM Christophe Leroy
> > <christophe.leroy@...roup.eu> wrote:
> >>
> >> This converts the architecture to GENERIC_CMDLINE.
> >>
> >> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> >> ---
> >>   arch/arm/Kconfig              | 38 +----------------------------------
> >>   arch/arm/kernel/atags_parse.c | 15 +++++---------
> >>   2 files changed, 6 insertions(+), 47 deletions(-)
> >>
> >> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> >> index 5da96f5df48f..67bc75f2da81 100644
> >> --- a/arch/arm/Kconfig
> >> +++ b/arch/arm/Kconfig
> >> @@ -50,6 +50,7 @@ config ARM
> >>          select GENERIC_ARCH_TOPOLOGY if ARM_CPU_TOPOLOGY
> >>          select GENERIC_ATOMIC64 if CPU_V7M || CPU_V6 || !CPU_32v6K || !AEABI
> >>          select GENERIC_CLOCKEVENTS_BROADCAST if SMP
> >> +       select GENERIC_CMDLINE if ATAGS
> >
> > Don't we need this enabled for !ATAGS (i.e. DT boot)?
> >
> > Can we always enable GENERIC_CMDLINE for OF_EARLY_FLATTREE?
> >
>
> Don't know.
>
> Today ARM has:
>
> choice
>         prompt "Kernel command line type" if CMDLINE != ""
>         default CMDLINE_FROM_BOOTLOADER
>         depends on ATAGS

I think that's a mistake. In a DT only case (no ATAGS), we'll get
different behaviour (in fdt.c) depending if CONFIG_ATAGS is enabled or
not. Note that at the time (2012) the above was added, the DT code
only supported CONFIG_CMDLINE and CONFIG_CMDLINE_FORCE.
CONFIG_CMDLINE_EXTEND was only added in 2016. And that has different
behavior for ATAGS vs. DT. In summary, it's a mess. We should drop the
depends either before this patch or just as part of this patch IMO.
I'd go with the latter given CONFIG_ATAGS is default y and enabled for
common configs. Without that, it looks like CONFIG_CMDLINE disappears
from menuconfig for at91_dt_defconfig.

Also, I think this code should be refactored a bit to eliminate
default_command_line. Instead, we should just save a pointer to the
ATAGS command line string, and then call cmdline_build here instead of
doing the extra copy:

        /* parse_early_param needs a boot_command_line */
        strlcpy(boot_command_line, from, COMMAND_LINE_SIZE);

Rob