linux-kernel - Re: [PATCH 5/5] RISC-V: Implement compile-time fixed mappings

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Date:   Sat, 19 Jan 2019 17:14:55 +0530
From:   Anup Patel <anup@...infault.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup.patel@....com>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Atish Patra <atish.patra@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 5/5] RISC-V: Implement compile-time fixed mappings

On Tue, Jan 15, 2019 at 7:17 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Mon, Jan 07, 2019 at 09:40:47PM +0530, Anup Patel wrote:
> > From: Anup Patel <anup.patel@....com>
> >
> > This patch implements compile-time virtual to physical
> > mappings. These compile-time fixed mappings can be used
> > by earlycon, ACPI, and early ioremap for creating fixed
> > mappings when FIX_EARLYCON_MEM=y.
> >
> > To start with, we have enabled compile-time fixed
> > mappings for earlycon.
> >
> > Signed-off-by: Anup Patel <anup.patel@....com>
> > ---
> >  arch/riscv/Kconfig              |  3 ++
> >  arch/riscv/include/asm/fixmap.h | 52 +++++++++++++++++++++++++++++++++
> >  arch/riscv/mm/init.c            | 32 ++++++++++++++++++++
> >  3 files changed, 87 insertions(+)
> >  create mode 100644 arch/riscv/include/asm/fixmap.h
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index e0d7d61779a6..66094aba9a59 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -86,6 +86,9 @@ config GENERIC_CSUM
> >  config GENERIC_HWEIGHT
> >       def_bool y
> >
> > +config FIX_EARLYCON_MEM
> > +     def_bool y
> > +
>
> Can you please throw in a prep patch to move FIX_EARLYCON_MEM to
> drivers/tty/serial/Kconfig and only select it from the architectures
> that use it?

Implementing fixmap is totally optional for architectures so it
makes sense to have FIX_EARLYCON_MEM as architecture
specific kconfig option. There are many such architecture specific
options provided as "def_bool y" in arch/<xyz>/Kconfig. Also,
having such "def_bool y" kconfig options in arch/<xyz>/Kconfig
gives us idea about optional features implemented by <xyz>
arch support.

I don't agree with this suggestion. If you still feel this is right way
to go then please go ahead and send patch to move
FIX_EARLYCON_MEM option in drivers/tty/serial/Kconfig.

>
> > + * fixmap.h: compile-time virtual memory allocation
>
> No need to mention the header name.

Sure, will remove header name.

>
> > + */
> > +
> > +#ifndef _ASM_RISCV_FIXMAP_H
> > +#define _ASM_RISCV_FIXMAP_H
> > +
> > +#ifndef __ASSEMBLY__
>
> As far as I can tell we never include this header from assembly files,
> so this ifdef should not be needed.
>
> > +/*
> > + * Here we define all the compile-time 'special' virtual
> > + * addresses. The point is to have a constant address at
> > + * compile time, but to set the physical address only
> > + * in the boot process.
> > + *
> > + * These 'compile-time allocated' memory buffers are
> > + * page-sized. Use set_fixmap(idx,phys) to associate
> > + * physical memory with fixmap indices.
> > + */
>
> Please use up the available 80 chars per line for comments.

Regards,
Anup