Re: [PATCH v2 2/2] dt-bindings: qcom: Update DT bindings for multiple DT

[Caleb Connolly]

Hi Amrit,

On 14/03/2024 12:11, Amrit Anand wrote:
> Qualcomm produces a lot of "unique" boards with slight differences in
> SoC's and board's configuration. For eg, there can be SM8150v1 on MTPv1,
> SM8150v1 on MTPv2, SM8150v2 on MTPv2, SM8150v2 on MTPv2 with a different
> PMIC, SM8150v2 with no modem support and so on. For instance, suppose we
> have 3 SoC, each with 4 boards supported, along with 2 PMIC support for
> each case which would lead to total of 24 DTB files. Along with these
> configurations, OEMs may also add certain additional board variants. Thus
> a mechanism is required to pick the correct DTB for the corresponding board.
> 
> Introduce mechanism to select required DTB using newly introduced device
> tree properties "board-id" and "board-id-type". "board-id" will contain
> the list of values of "qcom,soc-id", "qcom,board-id", "qcom,pmic-id" or
> "qcom,oem-id". "board-id-types" contains the type of parameter which is
> entered. It can be either "qcom,soc-id", "qcom,board-id", "qcom,pmic-id"
> or "qcom,oem-id".

Thanks for working on this, it's nice to finally see this logic
documented in the kernel.
> 
> Qualcomm based bootloader will use these properties to pick the best
> matched DTB to boot the device with.
> 
> Signed-off-by: Amrit Anand <quic_amrianan@xxxxxxxxxxx>
> ---
>  Documentation/devicetree/bindings/arm/qcom.yaml | 90 +++++++++++++++++++++++++
>  1 file changed, 90 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/arm/qcom.yaml b/Documentation/devicetree/bindings/arm/qcom.yaml
> index 7f80f48..dc66ae9 100644
> --- a/Documentation/devicetree/bindings/arm/qcom.yaml
> +++ b/Documentation/devicetree/bindings/arm/qcom.yaml
> @@ -1100,6 +1100,76 @@ properties:
>        kernel
>        The property is deprecated.
>  
> +  board-id:
> +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
> +    minItems: 2
> +    description: |
> +      Qualcomm specific bootloader uses multiple different identifiers
> +      (qcom,soc-id, qcom,board-id, qcom,pmic-id, qcom,oem-id) to select
> +      single Devicetree among list of Devicetrees. For different identifiers,
> +      the selection can be done either based on exact match (where the
> +      identifiers information coming from firmware should exactly match
> +      the ones described in devicetree) or best match (firmware provided
> +      identifier information closely matches with the one of the Devicetree).
> +      Below table describes matching criteria for each identifier::
> +      |----------------------------------------------------------------------|
> +      |  DT property  |  Individual fields   |   Exact  |  Best  |  Default  |
> +      |----------------------------------------------------------------------|
> +      | qcom,soc-id   |                                                      |
> +      |               |  Chipset Id          |     Y    |    N   |     -     |
> +      |               |  SoC Revision        |     N    |    Y   |     -     |
> +      | qcom,board-id |                                                      |
> +      |               |  Board Id            |     Y    |    N   |     -     |
> +      |               |  Board Major         |     N    |    Y   |     -     |
> +      |               |  Board Minor         |     N    |    Y   |     -     |
> +      |               |  Subtype             |     Y    |    N   |     0     |
> +      |               |  DDRtype             |     Y    |    N   |     0     |
> +      |               |  BootDevice Type     |     Y    |    N   |     0     |
> +      | qcom,pmic-id  |                                                      |
> +      |               |  Slave Id            |     Y    |    N   |     0     |
> +      |               |  PMIC Id             |     Y    |    N   |     0     |
> +      |               |  PMIC Major          |     N    |    Y   |     0     |
> +      |               |  PMIC Minor          |     N    |    Y   |     0     |
> +      | qcom,oem-id   |                                                      |
> +      |               |  OEM Id              |     Y    |    N   |     0     |
> +      |----------------------------------------------------------------------|
> +      For best match, identifiers are matched based on following priority order::
> +      SoC Revision > Board Major > Board Minor > PMIC Major > PMIC Minor
> +
> +  board-id-types:
> +    $ref: /schemas/types.yaml#/definitions/non-unique-string-array
> +    description:
> +       Each field and helper macros are defined at include/dt-bindings/arm/qcom,ids.
> +    minItems: 2
> +    items:
> +       oneOf:
> +         - const: qcom,soc-id
> +           description:
> +              Matches Qualcomm Technologies, Inc. boards with the specified SoC.
> +              2 integers are needed to describe a soc-id. The first integer is the
> +              SoC ID and the second integer is the SoC revision.
> +              qcom,soc-id = <soc-id  soc-revision>
> +         - const: qcom,board-id
> +           description: |
> +              Matches Qualcomm Technologies, Inc. boards with the specified board.
> +              2 integers are needed to describe a board-id. The first integer is the
> +              board ID. The second integer is the board-subtype.
> +              qcom,board-id = <board-id  board-subtype>
> +         - const: qcom,pmic-id
> +           description: |
> +              Qualcomm boards can be attached to multiple PMICs where slave-id (SID)
> +              indicates the address of the bus on which the PMIC is attached. It can be
> +              any number. The model for a PMIC indicates the PMIC name attached to bus
> +              described by SID along with  major and minor version. 2 integers are needed
> +              to describe qcom,pmic-id. The first integer is the slave-id and the second integer
> +              is the pmic model.
> +              qcom,pmic-id = <pmic-sid pmic-model>
> +         - const: qcom,oem-id
> +           description: |
> +              Matches Qualcomm Technologies, Inc. boards with the specified OEM ID.
> +              1 integer is needed to describe the oem-id.
> +              qcom,oem-id = <oem-id>
> +
>  allOf:
>    # Explicit allow-list for older SoCs. The legacy properties are not allowed
>    # on newer SoCs.
> @@ -1167,4 +1237,24 @@ allOf:
>  
>  additionalProperties: true
>  
> +examples:
> +  - |
> +    #include <dt-bindings/arm/qcom,ids.h>
> +    / {
> +         model = "Qualcomm Technologies, Inc. sc7280 IDP SKU1 platform";
> +         compatible = "qcom,sc7280-idp", "google,senor", "qcom,sc7280";
> +
> +         #board-id-cells = <2>;
> +         board-id = <QCOM_SOC_ID(SC7280) QCOM_SOC_REVISION(1)>,
> +                    <QCOM_SOC_ID(SC7280) QCOM_SOC_REVISION(2)>,
> +                    <QCOM_BOARD_ID(IDP, 1, 0) QCOM_BOARD_SUBTYPE(UFS, ANY, 1)>;
> +         board-id-types = "qcom,soc-id",
> +                          "qcom,soc-id",
> +                          "qcom,board-id";
Forgive me if this is a particularly cynical view, but this seems
incredibly blatant, the "qcom,board-id" property is deprecated for
various good reasons, just using a key/value map where "qcom,board-id"
is a key doesn't change that. There are two main issues I have with the
proposal here:

1. This breaks backwards compatibility, millions of production devices
with bootloaders that will never receive another update might be
compatible with the downstream "qcom,board-id" property, but they won't
work with this.
2. A top level board-id property that isn't namespaced implies that it
isn't vendor specific, but the proposed implementation doesn't even
pretend to be vendor agnostic.

U-Boot also has some ideas around this issue, there you can pass in
multiple DTBs and provide some board specific "best match" function.
I think there's definitely some value in exposing this information, but
there's no good reason to define the same data as `qcom,board-id` while
breaking production bootloaders.
> +
> +         #address-cells = <2>;
> +         #size-cells = <2>;
> +    };
> +
> +
>  ...

-- 
// Caleb (they/them)