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

[Rob Herring]

On Sat, Mar 25, 2017 at 11:31 PM, Bjorn Andersson
<bjorn.andersson@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
>> > ---
>> >
>> > 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?

Right.

>
>> > +
>> > +- 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@f9011000 {
>> > +           compatible = "syscon";
>>
>> syscon alone is not valid.
>>
>
> This is equivalent to how we have done this on all previous platforms.

Then they are wrong...

> 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.

Perhaps why we should get rid of syscon. It's not supposed to be a "I
don't know how to define a binding, so just make all registers
available for now".

I don't really see how a compatible string alone would create problems
to extend the binding if you need to later. Even if it did, you can
always rev compatible strings.

>> > +           reg = <0xf9011000 0x1000>;
>> > +   };
>> > +
>> > +   rpm_msg_ram: memory@68000 {
>> > +           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.

Properties such as?

>
> 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