linux-kernel - Re: [PATCH v2 3/7] powerpc: convert config files to generic cmdline

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Message-ID: <CAL_JsqKm76jRQYDcu3rGyUWKPLspoO=EZW_WFy=zAK+m_JYCTg@mail.gmail.com>
Date:   Wed, 24 Mar 2021 11:32:30 -0600
From:   Rob Herring <robh@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Daniel Walker <danielwa@...co.com>, Will Deacon <will@...nel.org>,
        Daniel Gimpelevich <daniel@...pelevich.san-francisco.ca.us>,
        Andrew Morton <akpm@...ux-foundation.org>,
        X86 ML <x86@...nel.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        xe-linux-external@...co.com, Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/7] powerpc: convert config files to generic cmdline

On Wed, Mar 24, 2021 at 11:01 AM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
>
>
> Le 09/03/2021 à 22:29, Daniel Walker a écrit :
> > On Tue, Mar 09, 2021 at 08:47:09AM +0100, Christophe Leroy wrote:
> >>
> >>
> >> Le 09/03/2021 à 01:02, Daniel Walker a écrit :
> >>> This is a scripted mass convert of the config files to use
> >>> the new generic cmdline. There is a bit of a trim effect here.
> >>> It would seems that some of the config haven't been trimmed in
> >>> a while.
> >>
> >> If you do that in a separate patch, you loose bisectability.
> >>
> >> I think it would have been better to do things in a different way, more or less like I did in my series:
> >> 1/ Provide GENERIC cmdline at the same functionnality level as what is
> >> spread in the different architectures
> >> 2/ Convert architectures to the generic with least churn.
> >> 3/ Add new features to the generic
> >
> > You have to have the churn eventually, no matter how you do it. The only way you
> > don't have churn is if you never upgrade the feature set.
> >
> >
> >>>
> >>> The bash script used to convert is as follows,
> >>>
> >>> if [[ -z "$1" || -z "$2" ]]; then
> >>>           echo "Two arguments are needed."
> >>>           exit 1
> >>> fi
> >>> mkdir $1
> >>> cp $2 $1/.config
> >>> sed -i 's/CONFIG_CMDLINE=/CONFIG_CMDLINE_BOOL=y\nCONFIG_CMDLINE_PREPEND=/g' $1/.config
> >>
> >> This is not correct.
> >>
> >> By default, on powerpc the provided command line is used only if the bootloader doesn't provide one.
> >>
> >> Otherwise:
> >> - the builtin command line is appended to the one provided by the bootloader
> >> if CONFIG_CMDLINE_EXTEND is selected
> >> - the builtin command line replaces to the one provided by the bootloader if
> >> CONFIG_CMDLINE_FORCE is selected
> >
> > I think my changes maintain most of this due to the override of
> > CONFIG_CMDLINE_PREPEND. This is an upgrade and the inflexibility in powerpc is
> > an example of why these changes were created in the first place.
>
> "inflexibility in powerpc" : Can you elaborate ?
>
> >
> > For example , say the default command line is "root=/dev/issblk0" from iss476
> > platform. And the bootloader adds "root=/dev/sda1"
> >
> > The result is <prepend><bootloader><append>.
>
>
> I'm still having hard time understanding the benefit of having both <prepend> and <append>.
> Could you please provide a complete exemple from real life, ie what exactly the problem is and what
> it solves ?

It doesn't matter. We already have both cases and 'extend' has meant either one.

What someone wants is policy and the kernel shouldn't be defining the policy.

Rob