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

[Christophe Leroy]

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 ?

> Then you have,
>
> root=/dev/issblk0 root=/dev/sda1
>
> and the bootloader has precedent over the default command line. So root= in the
> above cases is defined by the bootloader.
>
> The only issue would be if a person wants to override the default command line
> with an unrelated bootloader command line. I don't know how many people do this,
> but I doubt it's many. Can you think of any use cases like this?
>
> I would imagine there are many more people who have to entirely duplicate the
> default command line in the boot loader when they really just want to change a
> single part of it like the root= device or console device or speed.
>
> Daniel

Christophe