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

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Message-ID: <f085da86-8b6d-ba99-2d0a-736ec02424db@gmail.com>
Date:   Mon, 7 Jun 2021 12:26:21 +0200
From:   Johan Jonker <jbx6244@...il.com>
To:     wens@...nel.org
Cc:     Tianling Shen <cnsztl@...il.com>, 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 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.

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?

===

Johan

> 
> ChenYu
>