linux-kernel - Re: [PATCH v2 1/2] soc: qcom: Add device tree binding for GLINK RPM

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Date:   Sat, 25 Mar 2017 21:31:59 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Andy Gross <andy.gross@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-remoteproc@...r.kernel.org
Subject: Re: [PATCH v2 1/2] soc: qcom: Add device tree binding for GLINK RPM

On Fri 24 Mar 09:07 PDT 2017, Rob Herring wrote:

> On Mon, Mar 20, 2017 at 02:09:55PM -0700, Bjorn Andersson wrote:
> > Add device tree binding documentation for the Qualcomm GLINK RPM, used
> > for communication with the Resource Power Management subsystem in
> > various Qualcomm SoCs.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> > 
> > Changes since v1:
> > - None
> > 
> >  .../devicetree/bindings/soc/qcom/qcom,glink.txt    | 73 ++++++++++++++++++++++
> >  1 file changed, 73 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/soc/qcom/qcom,glink.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/soc/qcom/qcom,glink.txt b/Documentation/devicetree/bindings/soc/qcom/qcom,glink.txt
> > new file mode 100644
> > index 000000000000..da92c4f787f3
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/soc/qcom/qcom,glink.txt
> > @@ -0,0 +1,73 @@
> > +Qualcomm RPM GLINK binding
> > +
> > +This binding describes the Qualcomm RPM GLINK, a fifo based mechanism for
> > +communication with the Resource Power Management system on various Qualcomm
> > +platforms.
> > +
> > +- compatible:
> > +	Usage: required
> > +	Value type: <stringlist>
> > +	Definition: must be "qcom,glink-rpm"
> 
> SoC specific compatibles please.
> 

In addition to the generic qcom,glink-rpm I presume?

> > +
> > +- interrupts:
> > +	Usage: required
> > +	Value type: <prop-encoded-array>
> > +	Definition: should specify the IRQ used by the remote processor to
> > +		    signal this processor about communication related events
> > +
> > +- qcom,rpm-msg-ram:
> > +	Usage: required
> > +	Value type: <prop-encoded-array>
> > +	Definition: handle to RPM message memory resource
> > +
> > +- qcom,ipc:
> > +	Usage: required
> > +	Value type: <prop-encoded-array>
> > +	Definition: three entries specifying the outgoing ipc bit used for
> > +		    signaling the remote processor:
> > +		    - phandle to a syscon node representing the apcs registers
> > +		    - u32 representing offset to the register within the syscon
> > +		    - u32 representing the ipc bit within the register
> > +
> > += GLINK DEVICES
> > +Each subnode of the GLINK node represent function tied to a virtual
> > +communication channel. The name of the nodes are not important. The properties
> > +of these nodes are defined by the individual bindings for the specific function
> > +- but must contain the following property:
> > +
> > +- qcom,glink-channels:
> > +	Usage: required
> > +	Value type: <stringlist>
> > +	Definition: a list of channels tied to this function, used for matching
> > +		    the function to a set of virtual channels
> > +
> > += EXAMPLE
> > +The following example represents the GLINK RPM node on a MSM8996 device, with
> > +the function for the "rpm_request" channel defined, which is used for
> > +regualtors and root clocks.
> > +
> > +	apcs: syscon@...11000 {
> > +		compatible = "syscon";
> 
> syscon alone is not valid.
> 

This is equivalent to how we have done this on all previous platforms.
On previous platforms this generally maps to one of the "Krait Processor
SubSystem" blocks, so I'm quite worried with coming up with a compatible
for this block will not be compatible with any future description of
this block.

> > +		reg = <0xf9011000 0x1000>;
> > +	};
> > +
> > +	rpm_msg_ram: memory@...00 {
> > +		compatible = "qcom,rpm-msg-ram";
> 
> Is this more than just mmio-sram?
> 
> Or with a fixed use could be part of another node?
> 

It represents one of the RAM modules of one of the other ARM cores in
the SoC, used for shared memory communication with this ARM core. So the
hardware is essentially mmio-sram. But it has none of the properties
that a mmio-sram seem to have.

The reason I did not put it in the rpm-glink node is that in previous
Qualcomm platforms we have exactly the same system design, but the data
structure of the RAM was different, so it felt natural to just keep the
same description of the hardware.

> > +		reg = <0x68000 0x6000>;
> > +	};
> > +
> > +        rpm-glink {
> > +		compatible = "qcom,glink-rpm";
> > +
> > +		interrupts = <GIC_SPI 168 IRQ_TYPE_EDGE_RISING>;
> > +
> > +		qcom,rpm-msg-ram = <&rpm_msg_ram>;
> > +		qcom,ipc = <&apcs 0x10 0>;
> > +
> > +		rpm-requests {
> > +			compatible = "qcom,rpm-msm8996";
> > +			qcom,glink-channels = "rpm_requests";
> > +
> > +			...
> > +		};
> > +	};

Regards,
Bjorn