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

[Rafał Miłecki]

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 at milecki.pl>
>>
>> NVRAM structure contains device data and can be accessed using MMIO.
>>
>> Signed-off-by: Rafał Miłecki <rafal at milecki.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 at milecki.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.


> And it's a dedicated memory outside of regular RAM?

Yes