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References: <20221114194846.108814-1-detlev.casanova@collabora.com>
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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 14 Nov 2022 20:57:21 +0100
Message-ID: <CAMuHMdW9dAxJwzD=W1xLN2e_T_BNFk5MfbWh24Btur-o+-n4sg@mail.gmail.com>
Subject: Re: [PATCH] arm64: dts: renesas: r8a77951: Add reserved memory region
To:     Detlev Casanova <detlev.casanova@collabora.com>
Cc:     linux-kernel@vger.kernel.org, Magnus Damm <magnus.damm@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        "open list:ARM/RENESAS ARCHITECTURE" 
        <linux-renesas-soc@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>
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Hi Detlev,

On Mon, Nov 14, 2022 at 8:48 PM Detlev Casanova
<detlev.casanova@collabora.com> wrote:
> The 0x3000000 bytes memory region starting at 0x54000000 is
> reserved for the lossy_decompression hardware that will try to
> decompress any data written in the region.
>
> Mark the region as no-map to prevent linux from using it as RAM.
>
> Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>

Thanks for your patch!

> --- a/arch/arm64/boot/dts/renesas/r8a77951.dtsi
> +++ b/arch/arm64/boot/dts/renesas/r8a77951.dtsi
> @@ -290,6 +290,18 @@ CPU_SLEEP_1: cpu-sleep-1 {
>                 };
>         };
>
> +       reserved-memory {
> +               #address-cells = <2>;
> +               #size-cells = <2>;
> +               ranges;
> +
> +               /* device specific region for Lossy Decompression */
> +               lossy_decompress: memory-region@54000000 {
> +                       no-map;
> +                       reg = <0x00000000 0x54000000 0x0 0x03000000>;
> +               };
> +       };

This depends on the firmware/boot loader stack.  If it configures a
Lossy Decompression region, it should make sure to pass this
info through the various boot loader components to Linux,
just like is already done with the memory regions, RPC-IF state,
and OpTee configuration.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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