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

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Message-ID: <CAL_JsqKmUF_obwojLF1ia9+w7ba3yva2Vax=nth-BqKnirt99A@mail.gmail.com>
Date:   Thu, 25 Mar 2021 07:45:41 -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 Thu, Mar 25, 2021 at 6:06 AM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
>
>
> Le 24/03/2021 à 18:32, Rob Herring a écrit :
> > 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.
> >
>
> Ok, so you agree we don't need to provide two CMDLINE, one to be appended and one to be prepended.

Well, I wasn't thinking about that part of it, but yes as long as no
arch currently needs that.

> Let's only provide once CMDLINE as of today, and ask the user to select whether he wants it appended
> or prepended or replacee. Then no need to change all existing config to rename CONFIG_CMDLINE into
> either of the new ones.
>
> That's the main difference between my series and Daniel's series. So I'll finish taking Will's
> comment into account and we'll send out a v3 soon.

Great.

Rob