On 11/12, Rob Herring wrote:

On Mon, Oct 26, 2015 at 02:25:10PM -0700, Stephen Boyd wrote:

quoted

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).

Got a pointer to what these properties look like?

Do you mean the blob header format? You can see that described
in a text document next to the C file for dtbtool[1].

quoted

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.

Why does all this need to be a single property?

Because the different vendor properties were rejected by arm-soc
maintainers and the board compatible string was suggested as the
place to put such information.

quoted

+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 "<>"

[] brackets are more generally used for optional params.

Ok. I can make that change.

quoted

+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

Platform is pretty overloaded meaning. Perhaps board_type would be more 
clear.

Ok.

quoted

+
+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.

Can you define what these are exactly. I gather mb is RAM size.

Not really, foundry_id is a number and so is subtype.

quoted

+
+The 'panel' element must be one of the following strings:
+
+	720p
+	fWVGA
+	hd
+	qHD

How is this used?

I believe this was added so that we could have different dtbs for
devices that have different panels on them. I'm not sure this is
still used though. It could be legacy.

quoted

+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.

What is USID?

USID is Unique Slave IDentifier. It's an SPMI concept.

quoted

+
+Examples:
+
+	"qcom,msm8916-v1-cdp-pm8916-v2.1"
+
+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"

Which example is more common?

The former. I tried to make up the worst case example so we could
see how large the string may become.

[1] https://www.codeaurora.org/cgit/quic/la/device/qcom/common/tree/dtbtool/dtbtool.txt?h=LA.BF64.1.2.1.c1_rb1.30

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