Re: [PATCH v6 1/3] dt-bindings: soc: add mtk svs dt-bindings

[Roger Lu]

Hi Rob & Nicolas,

Sorry for the late reply.

On Mon, 2020-01-13 at 23:50 +0800, Rob Herring wrote:
> On Mon, Jan 13, 2020 at 12:44 AM Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote:
> >
> > On Thu, Jan 9, 2020 at 4:38 AM Rob Herring <robh@xxxxxxxxxx> wrote:
> > >
> > > On Tue, Jan 07, 2020 at 03:01:52PM +0800, Roger Lu wrote:
> > > > Document the binding for enabling mtk svs on MediaTek SoC.
> > > >
> > > > Signed-off-by: Roger Lu <roger.lu@xxxxxxxxxxxx>
> > > > ---
> > > >  .../devicetree/bindings/power/mtk-svs.txt     | 76 +++++++++++++++++++
> > > >  1 file changed, 76 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/power/mtk-svs.txt
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/power/mtk-svs.txt b/Documentation/devicetree/bindings/power/mtk-svs.txt
> > > > new file mode 100644
> > > > index 000000000000..9a3e81b9e1d2
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/power/mtk-svs.txt
> > > > @@ -0,0 +1,76 @@
> > > > +* Mediatek Smart Voltage Scaling (MTK SVS)
> > > > +
> > > > +This describes the device tree binding for the MTK SVS controller (bank)
> > > > +which helps provide the optimized CPU/GPU/CCI voltages. This device also
> > > > +needs thermal data to calculate thermal slope for accurately compensate
> > > > +the voltages when temperature change.
> > > > +
> > > > +Required properties:
> > > > +- compatible:
> > > > +  - "mediatek,mt8183-svs" : For MT8183 family of SoCs
> > > > +- reg: Address range of the MTK SVS controller.
> > > > +- interrupts: IRQ for the MTK SVS controller.
> > > > +- clocks, clock-names: Clocks needed for the svs hardware. required
> > > > +                       clocks are:
> > > > +                    "main": Main clock for svs controller to work.
> > > > +- nvmem-cells: Phandle to the calibration data provided by a nvmem device.
> > > > +- nvmem-cell-names: Should be "svs-calibration-data" and "calibration-data"
> > > > +
> > > > +Subnodes:
> > > > +- svs-cpu-little: SVS bank device node of little CPU
> > > > +  compatible: "mediatek,mt8183-svs-cpu-little"
> > > > +  operating-points-v2: OPP table hooked by SVS little CPU bank.
> > > > +                    SVS will optimze this OPP table voltage part.
> > > > +  vcpu-little-supply: PMIC buck of little CPU
> > > > +- svs-cpu-big: SVS bank device node of big CPU
> > > > +  compatible: "mediatek,mt8183-svs-cpu-big"
> > > > +  operating-points-v2: OPP table hooked by SVS big CPU bank.
> > > > +                    SVS will optimze this OPP table voltage part.
> > > > +  vcpu-big-supply: PMIC buck of big CPU
> > > > +- svs-cci: SVS bank device node of CCI
> > > > +  compatible: "mediatek,mt8183-svs-cci"
> > > > +  operating-points-v2: OPP table hooked by SVS CCI bank.
> > > > +                    SVS will optimze this OPP table voltage part.
> > > > +  vcci-supply: PMIC buck of CCI
> > > > +- svs-gpu: SVS bank device node of GPU
> > > > +  compatible: "mediatek,mt8183-svs-gpu"
> > > > +  operating-points-v2: OPP table hooked by SVS GPU bank.
> > > > +                    SVS will optimze this OPP table voltage part.
> > > > +  vgpu-supply: PMIC buck of GPU
> > > > +
> > > > +Example:
> > > > +
> > > > +     svs: svs@1100b000 {
> > > > +             compatible = "mediatek,mt8183-svs";
> > > > +             reg = <0 0x1100b000 0 0x1000>;
> > > > +             interrupts = <GIC_SPI 127 IRQ_TYPE_LEVEL_LOW>;
> > > > +             clocks = <&infracfg CLK_INFRA_THERM>;
> > > > +             clock-names = "main_clk";
> > > > +             nvmem-cells = <&svs_calibration>, <&thermal_calibration>;
> > > > +             nvmem-cell-names = "svs-calibration-data", "calibration-data";
> > > > +
> > > > +             svs_cpu_little: svs-cpu-little {
> > > > +                     compatible = "mediatek,mt8183-svs-cpu-little";
> > > > +                     operating-points-v2 = <&cluster0_opp>;
> > > > +                     vcpu-little-supply = <&mt6358_vproc12_reg>;
> > > > +             };
> > >
> > > I don't think this is a good binding. This information already exists
> > > elsewhere in the DT, so your driver should just look in those nodes.
> > > For example the regulator can be in the cpu nodes or the OPP table
> > > itself.
> >
> > Roger, if that helps, without changing any other binding, on 8183,
> > basically you could have:
> >  - svs-cpu-little: Add a handle to &cpu0 and get the regulator/opp
> > table from it.
> >  - svs-cpu-big: Handle to &cpu4
> 
> Why do you need those? Use the compatible of the cpus to determine big
> and little cores. Or there's the cpu capacity property that could be
> used instead.
> 
> >  - svs-cci: Handle to &cci
> 
> Is there more than 1 CCI? Just retrieve the node by the compatible.
> There's no need to have nodes that simply serve as a collection of
> data for some driver.
> 
> >  - svs-gpu: Handle to &gpu (BTW, it is expected that SVS would only
> > apply to vgpu/mali regulator, and not vsram regulator?)

svs-gpu depends on vgpu power on for init (don't care vgpu_sram). After
svs-gpu init is done, it doesn't need vgpu power on anymore. (vgpu can
be turned off)

Please allows me to introduce more about what svs-gpu device needs.
1. It needs gpu opp table from "gpu node" and gpu_core2 power-domains
from "gpu_core2 node". When svs-gpu has those resources, it turns on
gpu_core2 power-domain for svs-gpu-hw to have power (for calculating)
and svs-gpu-sw will update gpu opp table voltages' part.
2. Therefore, if I retrieve gpu-related node from phandle or compatible,
it means svs-gpu device in driver needs to attach two different gpu
nodes for attaining gpu opp table and gpu_core2 power-domains. I think
this architecture of svs-gpu confuses maintainer why it attaches two
different nodes instead of having a device to describe what it needs.
3. Is it acceptable to have a Linux device attaching two different
nodes? If yes, could you guide us some APIs for one device to attach two
nodes? I don't know how to implement it. Thanks.

> >
> > I'm not too sure how we'd fetch the right regulator name, however (for
> > the first 3 the name is "proc", for the last one it's "mali"), maybe
> > add a regulator-name list in the DT?
> 
> To put this another way, write an SoC specific driver that understands
> to some extent what exists in the SoC (and DT). I doubt something like
> this is going to be generic across more than a few SoCs at most.

> 
> Rob