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 <redacted>
---
 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"