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Subject: Re: [PATCH v5 02/31] powerpc/fadump: move internal code to a new file
To: Hari Bathini <hbathini@linux.ibm.com>,
 Michael Ellerman <mpe@ellerman.id.au>,
 linuxppc-dev <linuxppc-dev@ozlabs.org>
References: <156630261682.8896.3418665808003586786.stgit@hbathini.in.ibm.com>
 <156630266000.8896.13603358349585118846.stgit@hbathini.in.ibm.com>
 <871rwxskjo.fsf@mpe.ellerman.id.au>
 <7823769a-9e2c-9ae7-d12e-7d5e42f51355@linux.ibm.com>
From: Mahesh Jagannath Salgaonkar <mahesh@linux.vnet.ibm.com>
Date: Wed, 4 Sep 2019 14:32:00 +0530
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Cc: Ananth N Mavinakayanahalli <ananth@linux.ibm.com>,
 Mahesh J Salgaonkar <mahesh@linux.ibm.com>,
 Nicholas Piggin <npiggin@gmail.com>, Oliver <oohall@gmail.com>,
 Vasant Hegde <hegdevasant@linux.ibm.com>, Daniel Axtens <dja@axtens.net>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On 9/3/19 9:35 PM, Hari Bathini wrote:
> 
> 
> On 03/09/19 4:39 PM, Michael Ellerman wrote:
>> Hari Bathini <hbathini@linux.ibm.com> writes:
>>> Make way for refactoring platform specific FADump code by moving code
>>> that could be referenced from multiple places to fadump-common.c file.
>>>
>>> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
>>> ---
>>>  arch/powerpc/kernel/Makefile        |    2 
>>>  arch/powerpc/kernel/fadump-common.c |  140 ++++++++++++++++++++++++++++++++++
>>>  arch/powerpc/kernel/fadump-common.h |    8 ++
>>>  arch/powerpc/kernel/fadump.c        |  146 ++---------------------------------
>>>  4 files changed, 158 insertions(+), 138 deletions(-)
>>>  create mode 100644 arch/powerpc/kernel/fadump-common.c
>>
>> I don't understand why we need fadump.c and fadump-common.c? They're
>> both common/shared across pseries & powernv aren't they?
> 
> The convention I tried to follow to have fadump-common.c shared between fadump.c,
> pseries & powernv code while pseries & powernv code take callback requests from
> fadump.c and use fadump-common.c (shared by both platforms), if necessary to fullfil
> those requests...
> 
>> By the end of the series we end up with 149 lines in fadump-common.c
>> which seems like a waste of time. Just put it all in fadump.c.
> 
> Yeah. Probably not worth a new C file. Will just have two separate headers. One for
> internal code and one for interfacing with other modules...
> 
> [...]
> 
>>> + * Copyright 2019, IBM Corp.
>>> + * Author: Hari Bathini <hbathini@linux.ibm.com>
>>
>> These can just be:
>>
>>  * Copyright 2011, Mahesh Salgaonkar, IBM Corporation.
>>  * Copyright 2019, Hari Bathini, IBM Corporation.
>>
> 
> Sure.
> 
>>> + */
>>> +
>>> +#undef DEBUG
>>
>> Don't undef DEBUG please.
>>
> 
> Sorry! Seeing such thing in most files, I thought this was the convention. Will drop
> this change in all the new files I added.
> 
>>> +#define pr_fmt(fmt) "fadump: " fmt
>>> +
>>> +#include <linux/memblock.h>
>>> +#include <linux/elf.h>
>>> +#include <linux/mm.h>
>>> +#include <linux/crash_core.h>
>>> +
>>> +#include "fadump-common.h"
>>> +
>>> +void *fadump_cpu_notes_buf_alloc(unsigned long size)
>>> +{
>>> +	void *vaddr;
>>> +	struct page *page;
>>> +	unsigned long order, count, i;
>>> +
>>> +	order = get_order(size);
>>> +	vaddr = (void *)__get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
>>> +	if (!vaddr)
>>> +		return NULL;
>>> +
>>> +	count = 1 << order;
>>> +	page = virt_to_page(vaddr);
>>> +	for (i = 0; i < count; i++)
>>> +		SetPageReserved(page + i);
>>> +	return vaddr;
>>> +}
>>
>> I realise you're just moving this code, but why do we need all this hand
>> rolled allocation stuff?
> 
> Yeah, I think alloc_pages_exact() may be better here. Mahesh, am I missing something?

We hook up the physical address of this buffer to ELF core header as
PT_NOTE section. Hence we don't want these pages to be moved around or
reclaimed.

Thanks,
-Mahesh.