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Subject: Re: [PATCH] mm/memtest: Add ARCH_USE_MEMTEST
To:     Vladimir Murzin <vladimir.murzin@arm.com>, linux-mm@kvack.org
Cc:     Chris Zankel <chris@zankel.net>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linux-xtensa@linux-xtensa.org, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, Russell King <linux@armlinux.org.uk>,
        linux-mips@vger.kernel.org, Max Filippov <jcmvbkbc@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Paul Mackerras <paulus@samba.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org
References: <1612498242-31579-1-git-send-email-anshuman.khandual@arm.com>
 <a58f1a92-087d-cf90-ce2b-0c88b39a8116@arm.com>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <d6e9f640-e5c2-49b7-7ca9-ec6c3191e6f9@arm.com>
Date:   Mon, 8 Feb 2021 08:47:01 +0530
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On 2/5/21 2:50 PM, Vladimir Murzin wrote:
> Hi Anshuman,
> 
> On 2/5/21 4:10 AM, Anshuman Khandual wrote:
>> early_memtest() does not get called from all architectures. Hence enabling
>> CONFIG_MEMTEST and providing a valid memtest=[1..N] kernel command line
>> option might not trigger the memory pattern tests as would be expected in
>> normal circumstances. This situation is misleading.
> 
> Documentation already mentions which architectures support that:
> 
> memtest=        [KNL,X86,ARM,PPC] Enable memtest
> 
> yet I admit that not all reflected there

But there is nothing that prevents CONFIG_MEMTEST from being set on
other platforms that do not have an affect, which is not optimal.

> 
>>
>> The change here prevents the above mentioned problem after introducing a
>> new config option ARCH_USE_MEMTEST that should be subscribed on platforms
>> that call early_memtest(), in order to enable the config CONFIG_MEMTEST.
>> Conversely CONFIG_MEMTEST cannot be enabled on platforms where it would
>> not be tested anyway.
>>
> 
> Is that generic pattern? What about other cross arch parameters? Do they already
> use similar subscription or they rely on documentation?

Depending solely on the documentation should not be sufficient.

> 
> I'm not against the patch just want to check if things are consistent...
Not sure about other similar situations but those if present should
get fixed as well.