Re: [PATCH V7 2/4] Documentation: DT: bindings: Add power domain info for NVIDIA PMC

Thierry Reding
2016-03-07T10:28:17Z

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On Mon, Mar 07, 2016 at 10:00:58AM +0000, Jon Hunter wrote:
>
> On 05/03/16 04:31, Rob Herring wrote:
> > On Fri, Mar 04, 2016 at 12:23:04PM +0000, Jon Hunter wrote:
> >> Add power-domain binding documentation for the NVIDIA PMC driver in
> >> order to support generic power-domains.
> >>
> >> Signed-off-by: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> >> ---
> >> .../bindings/arm/tegra/nvidia,tegra20-pmc.txt | 80 ++++++++++++++++++++++
> >> 1 file changed, 80 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt
> >> index 53aa5496c5cf..7d52bbe99709 100644
> >> --- a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt
> >> +++ b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt
> >> @@ -1,5 +1,7 @@
> >> NVIDIA Tegra Power Management Controller (PMC)
> >>
> >> +== Power Management Controller Node ==
> >> +
> >> The PMC block interacts with an external Power Management Unit. The PMC
> >> mostly controls the entry and exit of the system from different sleep
> >> modes. It provides power-gating controllers for SoC and CPU power-islands.
> >> @@ -70,6 +72,11 @@ Optional properties for hardware-triggered thermal reset (inside 'i2c-thermtrip'
> >> Defaults to 0. Valid values are described in section 12.5.2
> >> "Pinmux Support" of the Tegra4 Technical Reference Manual.
> >>
> >> +Optional nodes:
> >> +- powergates : This node contains a hierarchy of power domain nodes, which
> >> + should match the powergates on the Tegra SoC. See "Powergate
> >> + Nodes" below.
> >> +
> >> Example:
> >>
> >> / SoC dts including file
> >> @@ -115,3 +122,76 @@ pmc@7000f400 {
> >> };
> >> ...
> >> };
> >> +
> >> +
> >> +== Powergate Nodes ==
> >> +
> >> +Each of the powergate nodes represent a power-domain on the Tegra SoC
> >> +that can be power-gated by the Tegra PMC. The name of the powergate node
> >> +should be one of the below. Note that not every powergate is applicable
> >> +to all Tegra devices and the following list shows which powergates are
> >> +applicable to which devices. Please refer to the Tegra TRM for more
> >> +details on the various powergates.
> >> +
> >> + Name Description Devices Applicable
> >> + 3d 3D Graphics Tegra20/114/124/210
> >> + 3d0 3D Graphics 0 Tegra30
> >> + 3d1 3D Graphics 1 Tegra30
> >> + aud Audio Tegra210
> >> + dfd Debug Tegra210
> >> + dis Display A Tegra114/124/210
> >> + disb Display B Tegra114/124/210
> >> + heg 2D Graphics Tegra30/114/124/210
> >> + iram Internal RAM Tegra124/210
> >> + mpe MPEG Encode All
> >> + nvdec NVIDIA Video Decode Engine Tegra210
> >> + nvjpg NVIDIA JPEG Engine Tegra210
> >> + pcie PCIE Tegra20/30/124/210
> >> + sata SATA Tegra30/124/210
> >> + sor Display interfaces Tegra124/210
> >> + ve2 Video Encode Engine 2 Tegra210
> >> + venc Video Encode Engine All
> >> + vdec Video Decode Engine Tegra20/30/114/124
> >> + vic Video Imaging Compositor Tegra124/210
> >> + xusba USB Partition A Tegra114/124/210
> >> + xusbb USB Partition B Tegra114/124/210
> >> + xusbc USB Partition C Tegra114/124/210
> >> +
> >> +Required properties:
> >> + - clocks: Must contain an entry for each clock required by the PMC for
> >> + controlling a power-gate. See ../clocks/clock-bindings.txt for details.
> >> + - resets: Must contain an entry for each reset required by the PMC for
> >> + controlling a power-gate. See ../reset/reset.txt for details.
> >> + - #power-domain-cells: Must be 0.
> >> +
> >> +Example:
> >> +
> >> + pmc: pmc@0,7000e400 {
> >
> > Just pmc@7000e400. We were erronously using commas for 64-bit addresses
> > briefly, but the correct usage is when there are distinct fields in reg
> > like PCI bus,dev,func.
>
> Ok. Looks like we use this style quite widely across all Tegra 32-bit
> and 64-bit devices for all peripheral devices.
>
> Thierry, Stephen,
>
> Do we need to correct this for existing devices?

"Need" is perhaps a little strong. It's unfortunate that back at the
time the existing format was deemed best practice, and now we're told
to have been doing it wrong all along. There's also the issue that in
practice somebody might use the node name for some sort of lookup in
userspace or whatever, and they'd have every right to do so, because
the DT is an ABI after all.

Technically removing the 0, from the unit address would be breaking
that ABI, but in practice I'd hope that we wouldn't really break the
world for any users. If this gets us on the same page as everyone
else, I'm fine with taking this risk. I've already begun to convert
existing device trees.

Fingers crossed that best practices won't change again...

Thierry

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