linux-kernel - Re: [PATCH stblinux.git 1/2] dt-bindings: firmware: add Broadcom's NVRAM memory mapping

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Message-ID: <5f4a50dc-0981-45b4-bb89-d6152689fe2a@gmail.com>
Date:   Mon, 8 Mar 2021 22:41:01 +0100
From:   Rafał Miłecki <zajec5@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Vivek Unune <npcomplete13@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        devicetree@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com,
        linux-kernel@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH stblinux.git 1/2] dt-bindings: firmware: add Broadcom's
 NVRAM memory mapping

On 08.03.2021 22:37, Rafał Miłecki wrote:
> On 08.03.2021 19:43, Rob Herring wrote:
>> On Tue, Mar 02, 2021 at 08:44:04AM +0100, Rafał Miłecki wrote:
>>> From: Rafał Miłecki <rafal@...ecki.pl>
>>>
>>> NVRAM structure contains device data and can be accessed using MMIO.
>>>
>>> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
>>> ---
>>>   .../bindings/firmware/brcm,nvram.yaml         | 41 +++++++++++++++++++
>>>   1 file changed, 41 insertions(+)
>>>   create mode 100644 Documentation/devicetree/bindings/firmware/brcm,nvram.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/firmware/brcm,nvram.yaml b/Documentation/devicetree/bindings/firmware/brcm,nvram.yaml
>>> new file mode 100644
>>> index 000000000000..12af8e2e7c9c
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/firmware/brcm,nvram.yaml
>>> @@ -0,0 +1,41 @@
>>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: "http://devicetree.org/schemas/firmware/brcm,nvram.yaml#"
>>> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
>>> +
>>> +title: Broadcom's NVRAM
>>> +
>>> +maintainers:
>>> +  - Rafał Miłecki <rafal@...ecki.pl>
>>> +
>>> +description: |
>>> +  NVRAM is a structure containing device specific environment variables.
>>> +  It is used for storing device configuration, booting parameters and
>>> +  calibration data.
>>
>> The structure of the data is fully discoverable just from a genericish
>> 'brcm,nvram'?
> 
> Yes, NVRAM structure is a header (with magic and length) and a list of
> key-value pairs separated by \0. If you map memory at given address you
> should verify magic and start reading key-value pairs.
> 
> Content example: foo=bar\0baz=qux\0quux(...)
> 
> There is no predefined order of pairs, set of keys or anything similar I
> could think of. I can't think of anything more worth describing in DT.

Ah, I've just realized, I'm replying to the "firmware" binding patch.

Florian suggested to look at NVMEM subsystem instead. Please kindly check
[PATCH V2 1/2] dt-bindings: nvmem: add Broadcom's NVRAM