linux-kernel - Re: [PATCH V6 09/22] LoongArch: Add boot and setup routines

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Date:   Tue, 8 Mar 2022 13:01:11 +0800
From:   Huacai Chen <chenhuacai@...il.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH V6 09/22] LoongArch: Add boot and setup routines

Hi, Mike,

On Tue, Mar 8, 2022 at 1:37 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> Hi,
>
> On Fri, Mar 04, 2022 at 08:43:03PM +0800, Huacai Chen wrote:
> > Hi, Mike,
> >
> > On Fri, Mar 4, 2022 at 6:49 PM Mike Rapoport <rppt@...nel.org> wrote:
> > >
> > > Hi,
> > >
> > >
> > > So ideally, the physical memory detection and registration should follow
> > > something like:
> > >
> > > * memblock_reserve() the memory used by firmware, kernel and initrd
> > > * detect NUMA topology
> > > * add memory regions along with their node ids to memblock.
> > >
> > > s390::setup_arch() is a good example of doing early reservations:
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/s390/kernel/setup.c#n988
> > I have a fast reading of S390, and I think we can do some adjust:
> > 1, call memblock_set_node(0, ULONG_MAX, &memblock.memory, 0) in
> > early_memblock_init().
> > 2, move memblock_reserve(PHYS_OFFSET, 0x200000) and
> > memblock_reserve(__pa_symbol(&_text), __pa_symbol(&_end) -
> > __pa_symbol(&_text)) to early_memblock_init().
> > 3, Reserve initrd memory in the first place.
> > It is nearly the same as the S390, then.
>
> It does not have to look like the same as s390 :)
> The important thing is to reserve all the memory before memblock
> allocations are possible.
New version is here, it's not completely the same as S390, but very similar:
https://lore.kernel.org/linux-arch/20220306112850.811504-1-chenhuacai@loongson.cn/T/#Z2e.:..:20220306112850.811504-10-chenhuacai::40loongson.cn:1arch:loongarch:kernel:mem.c

Firmware is not in SYSRAM regions, so we don't need to reserve them.
The first 2MB and the kernel region are reserved in
early_memblock_init(), before any allocations.

Initrd information is passed by cmdline, and initrd is now reserved
immediately after cmdline has parsed, by merging
init_initrd/finalize_initrd as you suggested:
https://lore.kernel.org/linux-arch/20220306112850.811504-1-chenhuacai@loongson.cn/T/#Z2e.:..:20220306112850.811504-10-chenhuacai::40loongson.cn:1arch:loongarch:kernel:setup.c

>
> > > > > > +early_param("memmap", early_parse_memmap);
> > > > >
> > > > > The memmap= processing is a hack indented to workaround bugs in firmware
> > > > > related to the memory detection. Please don't copy if over unless there is
> > > > > really strong reason.
> > > >
> > > > Hmmm, I have read the documents, most archs only support mem=limit,
> > > > but MIPS support mem=limit@...e. memmap not only supports
> > > > memmap=limit@...e, but also a lot of advanced syntax. LoongArch needs
> > > > both limit and limit@...e syntax. So can we make our code to support
> > > > only mem=limit and memmap=limit@...e, and remove all other syntax
> > > > here?
> > >
> > > The documentation describes what was there historically and both these
> > > options tend not to play well with complex memory layouts.
> > >
> > > If you must have them it's better to use x86 as an example rather than
> > > MIPS, just take into the account that on x86 memory always starts from 0,
> > > so they never needed to have a different base.
> > >
> > > For what use-cases LoongArch needs options?
> >
> > The use-case of limit@...e syntax is kdump, because our kernel is not
> > relocatable. I'll use X86 as an example.
>
> I missed that mem= can be used several times, so with MIPS implementation
> it's possible to define something like "mem=limit0@...e0 mem=limit1@...e1"
> and this will create two contiguous memory regions.
The new version is here:
https://lore.kernel.org/linux-arch/20220306112850.811504-1-chenhuacai@loongson.cn/T/#Z2e.:..:20220306112850.811504-10-chenhuacai::40loongson.cn:1arch:loongarch:kernel:setup.c
If I use the MIPS implementation, then memmap= is useless and can be
removed, but the MIPS implementation is not obey the rules in kernel
documents.

Huacai
>
> > Huacai
>
> --
> Sincerely yours,
> Mike.