linux-kernel - Re: [PATCH] MIPS: vpe-mt: provide a default 'physical

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Message-ID: <20230217115713.GA7701@alpha.franken.de>
Date:   Fri, 17 Feb 2023 12:57:13 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Philippe Mathieu-Daudé <philmd@...aro.org>,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>,
        Dengcheng Zhu <dzhu@...ecomp.com>,
        John Crispin <john@...ozen.org>, linux-mips@...r.kernel.org,
        Qais Yousef <qyousef@...alina.io>
Subject: Re: [PATCH] MIPS: vpe-mt: provide a default 'physical_memsize'

On Wed, Feb 15, 2023 at 10:59:35PM -0800, Randy Dunlap wrote:
> > I agree this is where this variable has be be declared / initialized,
> > but having this dependent on CONFIG_MIPS_MALTA/CONFIG_LANTIQ machines
> > doesn't seem right.
> 
> So far I have been able to consolidate the LANTIQ code into a general
> patch, but not MALTA.

if I didn't miss something physical_memory is always 0 for LANTIQ 
and something for MALTA depending on command line/DT. Now

arch/mips/kernel/vpe-mt.c contains

        /*
         * The sde-kit passes 'memsize' to __start in $a3, so set something
         * here...  Or set $a3 to zero and define DFLT_STACK_SIZE and
         * DFLT_HEAP_SIZE when you compile your program
         */
        mttgpr(6, v->ntcs);
        mttgpr(7, physical_memsize);

so the 0 for LANTIQ is fine with the correct VPE payload. But for
MALTA could cause major problems, if the VPE payload uses the top
of memory for it's stack. So I would guess nobody uses this "mode".
Therefore let's get rid of physical_memory in vpe.c completly.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]