linux-kernel - Re: [PATCH v2] MIPS: replace add_memory

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Message-ID: <20201012100117.GA6959@alpha.franken.de>
Date:   Mon, 12 Oct 2020 12:01:17 +0200
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Hauke Mehrtens <hauke@...ke-m.de>,
        Rafał Miłecki <zajec5@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        bcm-kernel-feedback-list@...adcom.com,
        "Maciej W. Rozycki" <macro@...ux-mips.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Keguang Zhang <keguang.zhang@...il.com>,
        John Crispin <john@...ozen.org>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] MIPS: replace add_memory_region with memblock

On Fri, Oct 09, 2020 at 05:15:37PM +0300, Serge Semin wrote:
> On Fri, Oct 09, 2020 at 02:07:52PM +0200, Thomas Bogendoerfer wrote:
> > On Thu, Oct 08, 2020 at 06:20:06PM +0300, Serge Semin wrote:
> > > > @@ -426,13 +387,14 @@ static int __init early_parse_memmap(char *p)
> > > >  
> > > >  	if (*p == '@') {
> > > >  		start_at = memparse(p+1, &p);
> > > > -		add_memory_region(start_at, mem_size, BOOT_MEM_RAM);
> > > > +		memblock_add(start_at, mem_size);
> > > >  	} else if (*p == '#') {
> > > >  		pr_err("\"memmap=nn#ss\" (force ACPI data) invalid on MIPS\n");
> > > >  		return -EINVAL;
> > > >  	} else if (*p == '$') {
> > > >  		start_at = memparse(p+1, &p);
> > > 
> > > > -		add_memory_region(start_at, mem_size, BOOT_MEM_RESERVED);
> > > > +		memblock_add(start_at, mem_size);
> > > > +		memblock_reserve(start_at, mem_size);
> > > 
> > > I suppose we could remove the memory addition from here too. What do you think?
> > 
> 
> > I'm not sure about that, add_memory_region() did a memblock_add
> > and then memblock_reserve for BOOT_MEM_RESERVED, that's why I changed
> > it that way.
> 
> The main question here whether we need to preserve the MIPS-specific semantics
> of the kernel 'memmap' parameter. Currently the memmap parameter passed with
> '$' specifier will be perceived as a reserved RAM region, while, for instance, 
> the same parameter on x86 will be converted to a region, which won't be
> registered in memblock at all, so the system won't be able to reuse it if it's
> needed to be (see parse_memmap_one() and e820__memblock_setup() for details).
> 
> I don't really know what approach is correct... 
> Documentation/admin-guide/kernel-parameters.txt isn't certain about that. It
> says that the region must be reserved, but no words whether it is supposed to be
> mappable or non-mappable.

I leave it as in v3 of the patch for now. If we come to the point what
the correct semantic should be, we can change it.

Thomas.

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