Re: [PATCH 1/3] devicetree: bindings: Document qcom board compatible format

[Olof Johansson]

Hi,

On Mon, Oct 26, 2015 at 2:25 PM, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> wrote:
> Some qcom based bootloaders identify the dtb blob based on a set
> of device properties like SoC, platform, PMIC, and revisions of
> those components. In downstream kernels, these values are added
> to the different component dtsi files (i.e. pmic dtsi file, SoC
> dtsi file, board dtsi file, etc.) via qcom specific DT
> properties. The dtb files are parsed by a program called dtbTool
> that picks out these properties and creates a table of contents
> binary blob with the property information and some offsets into
> the concatenation of all the dtbs (termed a QCDT image).
>
> The suggestion is to do this via the board compatible string
> instead, because these qcom specific properties are never used by
> the kernel. Add a document describing the format of the
> compatible string that encodes all this information that's
> currently encoded in the qcom,{msm-id,board-id,pmic-id}
> properties in downstream devicetrees. Future bootloaders may be
> updated to look at the compatible field instead of looking for
> the table of contents image. For non-updateable bootloaders, a
> new dtbTool program will parse the compatible string and generate
> a QCDT image from it.
>
> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> ---
>  Documentation/devicetree/bindings/arm/qcom.txt | 86 ++++++++++++++++++++++++++
>  1 file changed, 86 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/qcom.txt
>
> diff --git a/Documentation/devicetree/bindings/arm/qcom.txt b/Documentation/devicetree/bindings/arm/qcom.txt
> new file mode 100644
> index 000000000000..ed084367182d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/qcom.txt
> @@ -0,0 +1,86 @@
> +QCOM device tree bindings
> +-------------------------
> +
> +Some qcom based bootloaders identify the dtb blob based on a set of
> +device properties like SoC, platform, PMIC, and revisions of those components.
> +To support this scheme, we encode this information into the board compatible
> +string.
> +
> +Each board must specify a top-level board compatible string with the following
> +format:
> +
> +       compatible = "qcom,<SoC>(-<soc_version>)(-<foundry_id>)-<plat_type>(/<subtype>)(-<plat_version>)(-<mb>MB)(-<panel>-panel)(-boot-<boot>)(-<pmic>(-v<pmic_version>)){0-4}"
> +
> +where elements in parentheses "()" are optional and elements in brackets "<>"
> +are names of elements. Meaning only the 'SoC' and 'plat_type' elements are
> +required.
> +
> +The 'SoC' element must be one of the following strings:
> +
> +       apq8016
> +       apq8074
> +       apq8084
> +       apq8096
> +       msm8916
> +       msm8974
> +       msm8996
> +
> +The 'plat_type' element must be one of the following strings:
> +
> +       cdp
> +       liquid
> +       dragonboard
> +       mtp sbc
> +
> +
> +The 'soc_version', 'plat_version' and 'pmic_version' elements take the form of
> +v<Major>.<Minor> where the minor number may be omitted when it's zero, i.e.
> +v1.0 is the same as v1. If all versions of the 'plat_version' element's match,
> +then a wildcard '*' should be used, e.g. 'v*'.
> +
> +The 'foundry_id', 'subtype', and 'mb' elements are one or more digits from 0
> +to 9.
> +
> +The 'panel' element must be one of the following strings:
> +
> +       720p
> +       fWVGA
> +       hd
> +       qHD
> +
> +The 'boot' element must be one of the following strings:
> +
> +       emmc_sdc1
> +       ufs
> +
> +The 'pmic' element must be one of the following strings:
> +
> +       pm8841
> +       pm8019
> +       pm8110
> +       pma8084
> +       pmi8962
> +       pmd9635
> +       pm8994
> +       pmi8994
> +       pm8916
> +       pm8004
> +       pm8909
> +
> +The 'pmic' element is specified in order of ascending USID. The PMIC in USID0
> +goes first, and then USID2, USID4, and finally USID6. Up to four PMICs may be
> +specified and no holes in the USID number space are allowed.
> +
> +Examples:
> +
> +       "qcom,msm8916-v1-cdp-pm8916-v2.1"

This is just awkward, but this...

> +
> +A CDP board with an msm8916 SoC, version 1 paired with a pm8916 PMIC of version
> +2.1.
> +
> +       "qcom,apq8074-v2.0-2-dragonboard/1-v0.1-512MB-panel-qHD-boot-emmc_sdc1-pm8941-v0.2-pm8909-v2.2-pma8084-v3-pm8110-v1"

...this is just too much. It makes no sense to try to linearly
describe pretty much the whole hardware in the compatible string like
this when the information should be elsewhere in the DT.

If this is how it's done, why bother documenting the rest in device
tree at all? Why not just do a depth-first traversal of the DT and
create a string out of that and make that the compatible while you're
at it?

Consider this NAK:ed.


-Olof
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