linux-kernel - Re: [PATCH] sh: migor: Reserve memory block for CEU

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Date:   Wed, 8 Nov 2017 19:31:22 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sh: migor: Reserve memory block for CEU

Hi Jacopo,

On Wed, Nov 8, 2017 at 7:05 PM, Jacopo Mondi <jacopo+renesas@...ndi.org> wrote:
> A memory region for CEU video buffer has to be reserved during machine
> initialization.
>
> Originally, it was allocated through DMA API helpers and stored in the
> second IORESOURCE_MEM entry, to be later remapped by the CEU driver with
> a call to 'dma_declare_coherent_memory()'
>
> As Linux does not allow anymore to remap system RAM regions with
> 'memremap' function, sh_mobile_ceu driver fails when trying to remap the
> memory area:
>
> WARN_ONCE(1, "memremap attempted on ram %pa size: %#lx\n",
>           &offset, (unsigned long) size)
>
> from 'memremap()' function in kernel/memremap.c
>
> To avoid hitting that WARN_ONCE() and have memory successfully remapped,
> reserve a region using '.mv_mem_reserve' member of SH's 'struct
> sh_machine_vector' to make sure memory is reserved early enough, and
> removed from the available system RAM.
>
> This is similar to what happens on ARM architecture with
> 'arm_memblock_steal()' function.
>
> Suggested-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>

I assume this failure isnot limited to CEU on Migo-R, but applies to
the other 24
callers of platform_resource_setup_memory(), too?

Can platform_resource_setup_memory() be fixed instead, or is that difficult
due to the need to reserve the memory very early in the boot process?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds