linux-kernel - Re: [PATCH v9 2/8] dt-bindings: Introduce interconnect binding

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Message-ID: <b67253fb-d86d-2ddd-6c30-0833d6ed62ad@linaro.org>
Date:   Wed, 26 Sep 2018 17:42:15 +0300
From:   Georgi Djakov <georgi.djakov@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        rjw@...ysocki.net, mturquette@...libre.com, khilman@...libre.com,
        vincent.guittot@...aro.org, skannan@...eaurora.org,
        bjorn.andersson@...aro.org, amit.kucheria@...aro.org,
        seansw@....qualcomm.com, daidavid1@...eaurora.org,
        evgreen@...omium.org, mark.rutland@....com,
        lorenzo.pieralisi@....com, abailon@...libre.com,
        maxime.ripard@...tlin.com, arnd@...db.de,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v9 2/8] dt-bindings: Introduce interconnect binding

Hi Rob,

Thanks for the comments!

On 09/25/2018 09:02 PM, Rob Herring wrote:
> On Fri, Aug 31, 2018 at 05:01:45PM +0300, Georgi Djakov wrote:
>> This binding is intended to represent the relations between the interconnect
>> controllers (providers) and consumer device nodes. It will allow creating links
>> between consumers and interconnect paths (exposed by interconnect providers).
> 
> As I mentioned in person, I want to see other SoC families using this 
> before accepting. They don't have to be ready for upstream, but WIP 
> patches or even just a "yes, this works for us and we're going to use 
> this binding on X".

Other than the 3 Qualcomm SoCs (msm8916, msm8996, sdm845) that are
currently using this binding, there is ongoing work from at least two
other vendors that would be using this same binding. I will check on
what is their progress so far.

> Also, I think the QCom GPU use of this should be fully sorted out. Or 
> more generically how this fits into OPP binding which seems to be never 
> ending extended...

I see this as a further step. It could be OPP binding which include
bandwidth values or some separate DT property. Jordan has already
proposed something, do you have any initial comments on that?

BR,
Georgi

>> Signed-off-by: Georgi Djakov <georgi.djakov@...aro.org>
>> ---
>>  .../bindings/interconnect/interconnect.txt    | 60 +++++++++++++++++++
>>  1 file changed, 60 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/interconnect/interconnect.txt
>>
>> diff --git a/Documentation/devicetree/bindings/interconnect/interconnect.txt b/Documentation/devicetree/bindings/interconnect/interconnect.txt
>> new file mode 100644
>> index 000000000000..5cb7d3c8d44d
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/interconnect/interconnect.txt
>> @@ -0,0 +1,60 @@
>> +Interconnect Provider Device Tree Bindings
>> +=========================================
>> +
>> +The purpose of this document is to define a common set of generic interconnect
>> +providers/consumers properties.
>> +
>> +
>> += interconnect providers =
>> +
>> +The interconnect provider binding is intended to represent the interconnect
>> +controllers in the system. Each provider registers a set of interconnect
>> +nodes, which expose the interconnect related capabilities of the interconnect
>> +to consumer drivers. These capabilities can be throughput, latency, priority
>> +etc. The consumer drivers set constraints on interconnect path (or endpoints)
>> +depending on the use case. Interconnect providers can also be interconnect
>> +consumers, such as in the case where two network-on-chip fabrics interface
>> +directly
> 
> missing '.'
> 
>> +
>> +Required properties:
>> +- compatible : contains the interconnect provider compatible string
>> +- #interconnect-cells : number of cells in a interconnect specifier needed to
>> +			encode the interconnect node id
>> +
>> +Example:
>> +
>> +		snoc: snoc@...000 {
>> +			compatible = "qcom,msm8916-snoc";
>> +			#interconnect-cells = <1>;
>> +			reg = <0x580000 0x14000>;
>> +			clock-names = "bus_clk", "bus_a_clk";
>> +			clocks = <&rpmcc RPM_SMD_SNOC_CLK>,
>> +				 <&rpmcc RPM_SMD_SNOC_A_CLK>;
>> +		};
>> +
>> +
>> += interconnect consumers =
>> +
>> +The interconnect consumers are device nodes which dynamically express their
>> +bandwidth requirements along interconnect paths they are connected to. There
>> +can be multiple interconnect providers on a SoC and the consumer may consume
>> +multiple paths from different providers depending on use case and the
>> +components it has to interact with.
>> +
>> +Required properties:
>> +interconnects : Pairs of phandles and interconnect provider specifier to denote
>> +	        the edge source and destination ports of the interconnect path.
>> +
>> +Optional properties:
>> +interconnect-names : List of interconnect path name strings sorted in the same
>> +		     order as the interconnects property. Consumers drivers will use
>> +		     interconnect-names to match interconnect paths with interconnect
>> +		     specifiers.
> 
> specifier pairs.
> 
>> +
>> +Example:
>> +
>> +	sdhci@...4000 {
>> +		...
>> +		interconnects = <&pnoc MASTER_SDCC_1 &bimc SLAVE_EBI_CH0>;
>> +		interconnect-names = "ddr";
>> +	};