linux-kernel - Re: [PATCH v2 1/7] cmdline: Add generic function to build command line.

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Date:   Fri, 5 Mar 2021 12:33:00 -0600
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Will Deacon <will@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-arch@...r.kernel.org, robh@...nel.org,
        daniel@...pelevich.san-francisco.ca.us, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, danielwa@...co.com
Subject: Re: [PATCH v2 1/7] cmdline: Add generic function to build command line.

On Fri, Mar 05, 2021 at 10:58:02PM +1100, Michael Ellerman wrote:
> Will Deacon <will@...nel.org> writes:
> > That's very similar to us; we're not relocated, although we are at least
> > in control of the MMU (which is using a temporary set of page-tables).
> 
> prom_init runs as an OF client, with the MMU off (except on some Apple
> machines), and we don't own the MMU. So there's really nothing we can do :)

You *could* take over all memory mapping.  This is complex, and I
estimate the change you get this to work correctly on all supported
systems to be between -400% and 0%.

And not very long later Linux jettisons OF completely anyway.

> Though now that I look at it, I don't think we should be doing this
> level of commandline handling in prom_init. It should just grab the
> value from firmware and pass it to the kernel proper, and then all the
> prepend/append/force etc. logic should happen there.

That sounds much simpler, yes :-)


Segher