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

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Date:   Thu, 8 Oct 2020 18:54:54 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     "Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Rafał Miłecki <zajec5@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        bcm-kernel-feedback-list@...adcom.com,
        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 Thu, Oct 08, 2020 at 04:30:35PM +0100, Maciej W. Rozycki wrote:
> On Thu, 8 Oct 2020, Serge Semin wrote:
> 
> > At least I don't see a decent reason to preserve them. The memory registration
> > method does nearly the same sanity checks. The memory reservation function
> > defers a bit in adding the being reserved memory first. That seems redundant,
> > since the reserved memory won't be available for the system anyway. Do I miss
> > something?
> 

>  At the very least it serves informational purposes as it shows up in 
> /proc/iomem.

I thought about that, but /proc/iomem prints the System RAM up. Adding the reserved
memory regions to be just memory region first still seem redundant, since
reserving a non-reflected in memory region most likely indicates an erroneous
dts. I failed to find that, but do the kernel or DTC make sure that the reserved
memory regions has actual memory behind? (At least in the framework of the
memblock.memory vs memblock.reserved arrays or in the DT source file)

I also don't see the other platforms doing that, since the MIPS arch only
redefines these methods. So if a problem of adding a reserved memory with
possible no real memory behind exist, it should be fixed in the cross-platform
basis, don't you think?

-Sergey

> 
>   Maciej