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

Mike Rapoport
2022-03-05T20:09:48Z

On Sat, Mar 05, 2022 at 07:21:15PM +0000, Maciej W. Rozycki wrote:
> 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>.

You are right, and providing mem=X@Y for each contiguous memory range
should work even after 22 years.
I missed the fact that mem= can be repeated several times.

> 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.

This is sad indeed, but we still can update the kernel-parameters.txt with
a MIPS paragraph.

> Maciej

--
Sincerely yours,
Mike.