linux-kernel - Re: [REBASE PATCH v5 08/17] arm64: mm: Add dynamic ramoops region support through command line

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Message-ID: <14bf3fca-f031-d000-6fd6-d82f4de9b255@quicinc.com>
Date:   Wed, 13 Sep 2023 12:32:54 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     Will Deacon <will@...nel.org>
CC:     <corbet@....net>, <agross@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
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Subject: Re: [REBASE PATCH v5 08/17] arm64: mm: Add dynamic ramoops region
 support through command line

Thanks for the response.

On 9/12/2023 3:48 PM, Will Deacon wrote:
> On Mon, Sep 11, 2023 at 04:23:50PM +0530, Mukesh Ojha wrote:
>> The reserved memory region for ramoops is assumed to be at a fixed
>> and known location when read from the devicetree. This may not be
>> required for something like Qualcomm's minidump which is interested
>> in knowing addresses of ramoops region but it does not put hard
>> requirement of address being fixed as most of it's SoC does not
>> support warm reset and does not use pstorefs at all instead it has
>> firmware way of collecting ramoops region if it gets to know the
>> address and register it with apss minidump table which is sitting
>> in shared memory region in DDR and firmware will have access to
>> these table during reset and collects it on crash of SoC.
>>
>> So, add the support of reserving ramoops region to be dynamically
>> allocated early during boot if it is request through command line
>> via 'dyn_ramoops_size=' and fill up reserved resource structure and
>> export the structure, so that it can be read by ramoops driver.
>>
>> Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
>> ---
>>   arch/arm64/mm/init.c       | 94 ++++++++++++++++++++++++++++++++++++++++++++++
> 
> Why does this need to be in the arch code? There's absolutely nothing
> arm64-specific here.

Current clients of this cmdline would be only arm64, and that is the
reason of putting this here.

I was checking the places where memblock_phys_alloc_range() gets called
and found either it is arch/*/ and drivers/of/of_reserved_mem.c .

Since, this is not related to device tree, did not find a proper place
than this, i took the reference of this place from
reserve_crashkernel(). Also, not sure how could it be of help to other
non-arch64 users at this point.

-Mukesh
> 
> Will