On Thu, Oct 04, 2018 at 05:17:42PM -0500, Rob Herring wrote:

On Thu, Oct 4, 2018 at 2:17 PM Niklas Cassel [off-list ref] wrote:

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On Thu, Oct 04, 2018 at 10:18:22AM -0500, Rob Herring wrote:

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On Thu, Oct 4, 2018 at 3:36 AM Viresh Kumar [off-list ref] wrote:

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On 25-09-18, 14:43, Rob Herring wrote:

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On Tue, Sep 25, 2018 at 5:25 AM Rajendra Nayak [off-list ref] wrote:

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Hi Rob,

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+   rpmhpd_opp_table: opp-table {
+           compatible = "operating-points-v2-qcom-level";
+
+           rpmhpd_opp_ret: opp1 {
+                   qcom,level = <RPMH_REGULATOR_LEVEL_RETENTION>;
+           };

I don't see the point in using the OPP binding here when you aren't
using *any* of the properties from it.

Yeah, that's the case for now. But there are cases (as Stephen
mentioned earlier [1]) where the voltage values (and maybe other
values like current, etc) would be known and filled in DT. And that's
why we all agreed to use OPP tables for PM domains as well, as these
are really "operating performance points" of these PM domains.

Rob, are you fine with these bindings then?

Okay, my only thought is whether we should just use 'reg' here, or do
we need 'level' for anything else and should make it common?

I am not quite sure I understood what you are suggesting here :(

You could use the  'reg' property instead of 'qcom,level'. Any reason
not to do that?

They can use any property which uniquely identifies the OPP nodes in
the table. Though I never thought we can use 'reg' property in such a
way. I always thought it must be related to registers somehow :)

That's almost certainly where the name originates from back in the
90s. I view 'reg' as how you identify or address a device. This can be
channels of something like an ADC.

It's perhaps a stretch for OPP nodes as they aren't really a device,
but if the levels are part of the h/w then perhaps reg is a good
match.

FWIW, I actually have a use case on qcom SoCs.

I'm working on reviving an old patch series from Stephen Boyd:
https://lkml.org/lkml/2015/9/18/833


Rajendra's Documentation/devicetree/bindings/opp/qcom-opp.txt currently has:

Required properties:
- qcom,level: On Qualcomm platforms an OPP node can describe a positive value
representing a corner/level that's communicated with a remote microprocessor
(usually called the RPM) which then translates it into a certain voltage on
a voltage rail


I'm planning on extending it with something like:

Optional properties:
-qcom,fuse-level: On Qualcomm platforms, not all corners/levels are real
corners/levels, i.e., not all corners/levels have a unique eFuse associated.
Usually more than one corner/level uses the same eFuse corner/level.

Is that because there's additional parameters not covered as part of a corner?

Turns out that while qcom,fuse-level is a good idea for msm8916,
it will not suffice for msm8996.. Feel free to jump the the TL;DR below.


Looking at downstream, a corner is just something virtual:

https://source.codeaurora.org/quic/la/kernel/msm-3.10/tree/Documentation/devicetree/bindings/regulator/cpr-regulator.txt?h=msm-3.10#n362

In this example there are 9 virtual corners, but only 3 fuse-corners:

https://source.codeaurora.org/quic/la/kernel/msm-3.10/tree/arch/arm/boot/dts/qcom/msm8916-regulator.dtsi?h=msm-3.10#n90

qcom,cpr-corner-frequency-map = each frequency gets a virtual corner (probably
for simplicity).

qcom,cpr-corner-map = has a member for each virtual corner, defining what
fuse-corner each virtual corner really maps to.

Looking at the code:

https://source.codeaurora.org/quic/la/kernel/msm-3.10/tree/drivers/regulator/cpr-regulator.c?h=msm-3.10#n5460

These fuse-corners are really just efuses, where each fuse-corner
contains e.g. ref_uV, min_uV, max_uV.

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So for each OPP I would have:

opp1 {
        qcom,level = <foo>;
        qcom,fuse-level = <bar>;
}


Not sure if this changes your opinion about using reg,
but I thought that it was worth mentioning.

'reg' is probably not the right fit then.

Does any of this fuse-level apply to platforms using this binding? If
so, then it should be incorporated here. I don't want incomplete
bindings that get one property added at a time.

This binding is new, but Rajendra uses it for RPM in msm8996 and sdm845.

RPM does not need the fuse-corner property. (Not sure why it doesn't.)

Looking at the downstream CPR DT bindings for msm8996, they still have
a fuse-corner for each corner. However, the DT binding has changed
compared to msm8916. They now have:

https://source.codeaurora.org/quic/la/kernel/msm-4.4/tree/arch/arm/boot/dts/qcom/msm8996-regulator.dtsi?h=msm-4.4#n646

qcom,cpr-corner-fmax-map = array for each fuse-corner, defining the
maximum virtual corner that this fuse-corner maps to.

Each speed bin has a different number of supported OPPs.

In upstream we use opp-supported-hw, together with the speedbin efuse,
to determine what subset of OPPs the hardware supports.

The problem with msm8996, compared to msm8916, is that each speed bin
has its own qcom,cpr-corner-fmax-map.

So for msm8996, it will not be enough to simply have a single
qcom,fuse-level property for each OPP.
We could add a qcom,fuse-level property for each speedbin, for each OPP.

Like this:

opp1 {
     qcom,level = <foo>;
     qcom-fuse-level-speed0 = <bar>;
     qcom-fuse-level-speed1 = <bax>;
     qcom-fuse-level-speed2 = <baz>;
}



TL;DR:

Perhaps I should just try to add something like
qcom,cpr-corner-fmax-map, where there is an array per speedbin,
to Documentation/devicetree/bindings/opp/qcom-opp.txt
Like "compatible", it could be a property in the opp-table node.

Something like:

qcom,speed-bins = <3>;
qcom,fuse-level-to-max-level-map =
					/* Speed bin 0 */
					<1 2 7 12 16>,

					/* Speed bin 1 */
					<1 2 7 12 13>,

					/* Speed bin 2 */
					<1 2 7 12 16>;

Since this would work for both msm8916 and msm8996.
And this way you could still change qcom,level to use
reg if you want.


Kind regards,
Niklas