Re: [PATCH] arm64: dts: renesas: sparrow-hawk: Reserve first 128 MiB of DRAM

[Geert Uytterhoeven]

Hi Marek,

On Tue, 24 Mar 2026 at 15:33, Marek Vasut
<marek.vasut+renesas@xxxxxxxxxxx> wrote:
> Mark the first 128 MiB of DRAM as reserved. The first 128 MiB of DRAM
> may optionally be used by TFA and other firmware for its own purposes,
> and in such case, Linux must not use this memory.
>
> On this platform, U-Boot runs in EL3 and starts TFA BL31 and Linux from
> a single combined fitImage. U-Boot has full access to all memory in the
> 0x40000000..0xbfffffff range, as well memory in the memory banks in the
> 64-bit address ranges, and therefore U-Boot patches this full complete
> view of platform memory layout into the DT that is passed to the next
> stage.
>
> The next stage is TFA BL31 and then the Linux kernel. The TFA BL31 does
> not modify the DT passed from U-Boot to TFA BL31 and then to Linux with
> any new reserved-memory {} node to reserve memory areas used by the TFA
> BL31 to prevent the next stage from using those areas, which lets Linux
> to use all of the available DRAM as described in the DT that was passed
> in by U-Boot, including the areas that are newly utilized by TFA BL31.
>
> In case of high DRAM utilization, for example in case of four instances
> of "memtester 3900M" running in parallel, unless the memory used by TFA
> BL31 is properly reserved, Linux may use and corrupt the memory used by
> TFA BL31, which would often lead to system becoming unresponsive.
>
> Until TFA BL31 can properly fill its own reserved-memory node into the
> DT, and to assure older versions of TFA BL31 do not cause problems, add
> explicitly reserved-memory {} node which prevents Linux from using the
> first 128 MiB of DRAM.
>
> Note that TFA BL31 can be adjusted to use different memory areas, this
> newly added reserved-memory {} node follows longer-term practice on the
> R-Car SoCs where the first 128 MiB of DRAM is reserved for firmware use.
> In case user does modify TFA BL31 to use different memory ranges, they
> must either use a future version of TFA BL31 which properly patches a
> reserved-memory {} node into the DT, or they must adjust the address
> ranges of this reserved-memory {} node accordingly.
>
> Fixes: a719915e76f2 ("arm64: dts: renesas: r8a779g3: Add Retronix R-Car V4H Sparrow Hawk board support")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Marek Vasut <marek.vasut+renesas@xxxxxxxxxxx>

Thanks for your patch!

> --- a/arch/arm64/boot/dts/renesas/r8a779g3-sparrow-hawk.dts
> +++ b/arch/arm64/boot/dts/renesas/r8a779g3-sparrow-hawk.dts
> @@ -118,6 +118,17 @@ memory@600000000 {
>                 reg = <0x6 0x00000000 0x1 0x00000000>;
>         };
>
> +       reserved-memory {
> +               #address-cells = <2>;
> +               #size-cells = <2>;
> +               ranges;
> +
> +               tfa@40000000 {
> +                       reg = <0x0 0x40000000 0x0 0x8000000>;
> +                       no-map;
> +               };
> +       };

Obviously I don't like this very much, but I agree there is not much
else we can do at this point.  Shall I add a

    /* Temporary workaround for broken TFA BL31 */

comment while applying?

Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
i.e. will queue in renesas-fixes for v7.0.

> +
>         /* Page 27 / DSI to Display */
>         dp-con {
>                 compatible = "dp-connector";

Gr{oetje,eeting}s,

                        Geert

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

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