linux-kernel - Re: [PATCH 1/2] dt-bindings: hwinfo: Introduce board-id

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Date: Wed, 24 Jan 2024 18:12:28 +0530
From: Amrit Anand <quic_amrianan@...cinc.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <agross@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>
CC: <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <kernel@...cinc.com>,
        Elliot Berman
	<quic_eberman@...cinc.com>
Subject: Re: [PATCH 1/2] dt-bindings: hwinfo: Introduce board-id


On 1/23/2024 5:39 PM, Krzysztof Kozlowski wrote:
> On 20/01/2024 12:20, Amrit Anand wrote:
>> From: Elliot Berman <quic_eberman@...cinc.com>
>>
>
>
>> How is this better than Qualcomm's qcom,msm-id/qcom,board-id?
>> -------------------------------------------------------------
>> The selection process for devicetrees was Qualcomm-specific and not
>> useful for other devices and bootloaders that were not developed by
>> Qualcomm because a complex algorithm was used to implement. Board-ids
>> provide a matching solution that can be implemented by bootloaders
>> without introducing vendor-specific code. Qualcomm uses three
>> devicetree properties: msm-id (interchangeably: soc-id), board-id, and
>> pmic-id.  This does not scale well for use casese which use identifiers,
>> for example, to distinguish between a display panel. For a display
>> panel, an approach could be to add a new property: display-id,
>> but now	bootloaders need to be updated to also read this property. We
>> want to	avoid requiring to update bootloaders with new hardware
> Some mis-indentation in two lines above.
Sure will take care of this.
>
>> identifiers: a bootloader need only recognize the identifiers it can
>> handle.
>>
>> Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>
>> Signed-off-by: Amrit Anand <quic_amrianan@...cinc.com>
>> ---
>>   .../devicetree/bindings/hwinfo/board-id.yaml       | 53 ++++++++++++++++++++++
>>   1 file changed, 53 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/hwinfo/board-id.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/hwinfo/board-id.yaml b/Documentation/devicetree/bindings/hwinfo/board-id.yaml
> I think we should add it to dtschema, because bootloaders are using these.
Do you want us to move this file completely to the below mentioned repo 
and under which directory?
https://github.com/devicetree-org/dt-schema

>
>> new file mode 100644
>> index 0000000..82d5ff7
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/hwinfo/board-id.yaml
>> @@ -0,0 +1,53 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/hwinfo/board-id.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Board Identifier for Devicetree Selection
>> +
>> +maintainers:
>> +  - Amrit Anand <quic_amrianan@...cinc.com>
>> +  - Elliot Berman <quic_eberman@...cinc.com>
>> +
>> +description: |
> Do not need '|' unless you need to preserve formatting.
Will drop it.
>
>> +  Device manufacturers frequently ship multiple boards under a single
>> +  software package. These software packages will ship multiple devicetree
>> +  blobs and require some mechanism to pick the correct DTB for the board
>> +  the software package was deployed. board-id provides a mechanism for
>> +  bootloaders to select the appropriate DTB which is vendor/OEM-agnostic.
>> +
>> +select:
>> +  anyOf:
>> +    - required:
>> +        - 'board-id'
>> +    - required:
>> +        - 'board-id-types'
>> +    - required:
>> +        - '#board-id-cells'
> I don't fully get why do you need this select. Isn't the schema selected
> by nodename? Or maybe it is for the final required: but then this could
> be just set of dependencies.
The nodename here would be "/". So it will be applied to all the DTs, right?
Here, we wanted this to apply only if the above mentioned properties are 
present.
Do you suggest moving this to qcom,board-id.yaml and the required: as well.
So that vendor specific yaml could be applied?
>> +
>> +properties:
>> +  $nodename:
>> +    const: "/"
> Blank line.
Will add it.
>> +  board-id:
>> +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
>> +    description: |
> Do not need '|' unless you need to preserve formatting.
Ack
>> +      A list of identifiers that can be used to match with this devicetree.
> s/devicetree/Devicetree/ ?
Will update
>> +      The interpretatation of each cell can be matched with the
> Typo: interpretation
Will update
>> +      board-id-type at the same index.
>> +
>> +  board-id-types:
>> +    $ref: /schemas/types.yaml#/definitions/non-unique-string-array
>> +    description:
>> +      Defines the type of each cell, indicating to the DeviceTree selection
> s/DeviceTree/Devicetree/ ?
Will update
>
>> +      mechanism how to parse the board-id.
>> +
>> +  '#board-id-cells':
>   What are the cells for?
Bootloader will use this to check the number of entries in a tuple of 
board-id.
Vendors can have different logic in bootloader to specify the number
So wanted to make it flexible.

Thanks,
Amrit.