linux-kernel - Re: [PATCH] arm64: dts: rockchip: add EEPROM node for NanoPi R4S

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Date:   Tue, 8 Jun 2021 00:01:17 +0800
From:   Tianling Shen <cnsztl@...il.com>
To:     Johan Jonker <jbx6244@...il.com>
Cc:     Chen-Yu Tsai <wens@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Marty Jones <mj8263788@...il.com>, Pavel Machek <pavel@....cz>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: rockchip: add EEPROM node for NanoPi R4S

Hi Johan,

On Mon, Jun 7, 2021 at 6:26 PM Johan Jonker <jbx6244@...il.com> wrote:
>
> Hi Chen-Yu,
>
> On 6/7/21 11:40 AM, Chen-Yu Tsai wrote:
> > On Mon, Jun 7, 2021 at 5:31 PM Johan Jonker <jbx6244@...il.com> wrote:
> >>
> >> Hi Tianling,
> >>
> >> On 6/7/21 10:17 AM, Tianling Shen wrote:
> >>> NanoPi R4S has a EEPROM attached to the 2nd I2C bus (U92), which
> >>> stores the MAC address.
> >>>
> >>> Signed-off-by: Tianling Shen <cnsztl@...il.com>
> >>> ---
> >>>  arch/arm64/boot/dts/rockchip/rk3399-nanopi-r4s.dts | 9 +++++++++
> >>>  1 file changed, 9 insertions(+)
> >>>
> >>> diff --git a/arch/arm64/boot/dts/rockchip/rk3399-nanopi-r4s.dts b/arch/arm64/boot/dts/rockchip/rk3399-nanopi-r4s.dts
> >>> index cef4d18b599d..4a82f50a07c5 100644
> >>> --- a/arch/arm64/boot/dts/rockchip/rk3399-nanopi-r4s.dts
> >>> +++ b/arch/arm64/boot/dts/rockchip/rk3399-nanopi-r4s.dts
> >>> @@ -68,6 +68,15 @@
> >>>       status = "disabled";
> >>>  };
> >>>
> >>> +&i2c2 {
> >>> +     eeprom@51 {
> >>> +             compatible = "microchip,24c02", "atmel,24c02";
> >>> +             reg = <0x51>;
> >>> +             pagesize = <16>;
> >>
> >>> +             read-only; /* This holds our MAC */
> >>
> >> The mainline dts files should be generic I think.
> >> Any comment about "use", partitions or write ability should be avoided.
> >> It's up the user.
> >
>
> > Per the datasheet for this specific EEPROM, the latter half (128 bytes)
> > is read-only in hardware by design though.
>
> The 24AA02XEXX is programmed at the factory with a
> globally unique node address stored in the upper half
> of the array and permanently write-protected. The
> remaining 1,024 bits are available for application use.
>

In my opinion, as this contains data programmed by the factory, would
it be okay to keep it read-only?

> Just a question...
>
>     nvmem-cells = <&mac_address>;
>     nvmem-cells-names = "mac-address";
>
> Which part does this point to?
>
> Can we use the lower part to store/rewrite this too?
>
> ===
>
> From at24.yaml:
>
>             items:
>               - pattern:
> "^(atmel|catalyst|microchip|nxp|ramtron|renesas|rohm|st),(24(c|cs|lc|mac)[0-9]+|spd)$"
>               - pattern: "^atmel,(24(c|cs|mac)[0-9]+|spd)$"
>
> How does Microchip 24AA025E48 fit the regex?
> What compatible would you advise?

It seems that 24AA025E48 is a variant of 24MAC402 [1], and
`atmel,24c02` will be okay in this case.
1. https://lkml.org/lkml/2018/1/24/494

Thanks,
Tianling.

>
> ===
>
> Johan
>
> >
> > ChenYu
> >