linux-kernel - Re: [PATCH v4 0/4] MIPS: Modify mem= and memmap= parameter

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Message-ID: <alpine.DEB.2.21.2203051837280.47558@angie.orcam.me.uk>
Date:   Sat, 5 Mar 2022 19:21:15 +0000 (GMT)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Mike Rapoport <rppt@...nel.org>
cc:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/4] MIPS: Modify mem= and memmap= parameter

On Sat, 5 Mar 2022, Mike Rapoport wrote:

> > >  For example I have an x86 system that Linux does not how to interrogate
> > > for RAM beyond 64MiB, so I do use `memmap=128M@0' (for legacy reasons the
> > > x86 platform has a special exception to always exclude area between 640K
> > > and 1M from being used even if not explicitly specified, but we do not
> > > have a need for such legacy such legacy concerns with the MIPS port).  I
> > > consider it an interim measure however until the kernel has been fixed.
> > > 
> > >   Maciej
> > > 
> > 
> > Hi Mike, Thomas and Maciej,
> > 
> > Thank you very much for your feedbacks and discussions.
> > 
> > To be frank, I think mem= and memmap= are used for debugging and testing
> > in most cases, the intention of this patchset is to refactor the related
> > code to make them work well on mips.
> 
> mem= works fine on mips and there is no need to change it.
> 
> If you must supply complex memory layout on the command line, consider
> implementing support for memmap=exact and multiple memmap= parameters on
> the kernel command line, like x86 does.

 There's nothing to implement as the MIPS port has supported arbitrary 
memory maps since Dec 11th, 2000; that's almost 22 years now.  C.f.: 
<https://lore.kernel.org/linux-mips/Pine.GSO.3.96.1000814133957.7256S-100000@delta.ds2.pg.gda.pl/>, 
<https://git.kernel.org/pub/scm/linux/kernel/git/ralf/linux.git/commit/?id=97b7ae4257ef>.

 Sadly commit a09fc446fb6d ("[MIPS] setup.c: use early_param() for early 
command line parsing") removed last pieces of inline documentation; I 
don't know why things like that get approved, but neither I can take 
responsibility.

 Also to say (in said commit):

"There's no point to rewrite some logic to parse command line
to pass initrd parameters or to declare a user memory area.
We could use instead parse_early_param() that does the same
thing."

is IMHO unfair given that the "rewrite" was there in place almost six 
years before `parse_early_param' even started to exist!  Why do people 
assume things have always been like they see them at the time they look?

  Maciej