linux-kernel - Re: [PATCH 3/6] ARM: dts: bcm2711: Add reserved memory template to hold firmware configuration

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Message-ID: <CAL_JsqLSnGzJgEtJBVQqR7jY2bvxCfC-84u-GR-V8htw_O60JQ@mail.gmail.com>
Date:   Tue, 15 Dec 2020 14:27:09 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        devicetree@...r.kernel.org,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>
Subject: Re: [PATCH 3/6] ARM: dts: bcm2711: Add reserved memory template to
 hold firmware configuration

On Tue, Dec 15, 2020 at 9:56 AM Nicolas Saenz Julienne
<nsaenzjulienne@...e.de> wrote:
>
> RPi4's co-processor will copy the board's bootloader configuration into
> memory for the OS to consume. Introduce a reserved-memory area template
> for the co-processor to edit before booting the system so as for Linux
> not to overwrite that memory.
>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> ---
>  arch/arm/boot/dts/bcm2711-rpi-4-b.dts | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> index 403bacf986eb..c58e58e8ce39 100644
> --- a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> +++ b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> @@ -25,6 +25,7 @@ aliases {
>                 emmc2bus = &emmc2bus;
>                 ethernet0 = &genet;
>                 pcie0 = &pcie0;
> +               eeprom = &eeprom;

I don't see the need for this...

>         };
>
>         leds {
> @@ -218,6 +219,19 @@ &pwm1 {
>         status = "okay";
>  };
>
> +&rmem {
> +       /*
> +        * RPi4's co-processor will copy the board's bootloader configuration
> +        * into memory for the OS to consume. It'll also update this node with
> +        * its placement information.
> +        */
> +       eeprom: eeprom@0 {

But it's not an eeprom. It's just memory with some format to the contents.

> +               reg = <0x0 0x0 0x0>;
> +               no-map;
> +               status = "disabled";
> +       };
> +};
> +
>  /* SDHCI is used to control the SDIO for wireless */
>  &sdhci {
>         #address-cells = <1>;
> --
> 2.29.2
>