linux-kernel - Re: [PATCH v7 1/2] dt-bindings: cpufreq: Introduce QCOM CPUFREQ Firmware bindings

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Date:   Tue, 07 Aug 2018 23:15:02 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>,
        Taniya Das <tdas@...eaurora.org>, skannan@...eaurora.org
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Amit Nischal <anischal@...eaurora.org>,
        devicetree@...r.kernel.org, robh@...nel.org,
        amit.kucheria@...aro.org, evgreen@...gle.com
Subject: Re: [PATCH v7 1/2] dt-bindings: cpufreq: Introduce QCOM CPUFREQ Firmware
 bindings

Quoting Taniya Das (2018-08-07 19:46:01)
> 
> 
> On 8/8/2018 12:54 AM, skannan@...eaurora.org wrote:
> > On 2018-08-07 04:12, Sudeep Holla wrote:
> >> On Mon, Aug 06, 2018 at 01:54:24PM -0700, skannan@...eaurora.org wrote:
> >>> On 2018-08-03 16:46, Stephen Boyd wrote:
> >>> >Quoting Taniya Das (2018-07-24 03:42:49)
> >>> >>diff --git
> >>> >>a/Documentation/devicetree/bindings/cpufreq/cpufreq-qcom-hw.txt
> >>> >>b/Documentation/devicetree/bindings/cpufreq/cpufreq-qcom-hw.txt
> >>> >>new file mode 100644
> >>> >>index 0000000..22d4355
> >>> >>--- /dev/null
> >>> >>+++ b/Documentation/devicetree/bindings/cpufreq/cpufreq-qcom-hw.txt
> >>> >>@@ -0,0 +1,172 @@
> >>> >[...]
> >>> >>+
> >>> >>+               CPU7: cpu@700 {
> >>> >>+                       device_type = "cpu";
> >>> >>+                       compatible = "qcom,kryo385";
> >>> >>+                       reg = <0x0 0x700>;
> >>> >>+                       enable-method = "psci";
> >>> >>+                       next-level-cache = <&L2_700>;
> >>> >>+                       qcom,freq-domain = <&freq_domain_table1>;
> >>> >>+                       L2_700: l2-cache {
> >>> >>+                               compatible = "cache";
> >>> >>+                               next-level-cache = <&L3_0>;
> >>> >>+                       };
> >>> >>+               };
> >>> >>+       };
> >>> >>+
> >>> >>+       qcom,cpufreq-hw {
> >>> >>+               compatible = "qcom,cpufreq-hw";
> >>> >>+
> >>> >>+               clocks = <&rpmhcc RPMH_CXO_CLK>;
> >>> >>+               clock-names = "xo";
> >>> >>+
> >>> >>+               #address-cells = <2>;
> >>> >>+               #size-cells = <2>;
> >>> >>+               ranges;
> >>> >>+               freq_domain_table0: freq_table0 {
> >>> >>+                       reg = <0 0x17d43000 0 0x1400>;
> >>> >>+               };
> >>> >>+
> >>> >>+               freq_domain_table1: freq_table1 {
> >>> >>+                       reg = <0 0x17d45800 0 0x1400>;
> >>> >>+               };
> >>> >
> >>> >Sorry, this is just not proper DT design. The whole node should have a
> >>> >reg property, and it should contain two (or three if we're handling the
> >>> >L3 clk domain?) different offsets for the different power clusters. The
> >>> >problem seems to still be that we don't have a way to map the CPUs to
> >>> >the clk domains they're in provided by this hardware block. Making
> >>> >subnodes is not the solution.
> >>>
> >>> The problem is mapping clock domains to logical CPUs that CPUfreq 
> >>> uses. The
> >>> physical CPU to logical CPU mapping can be changed by the kernel (even
> >>> through DT if I'm not mistaken). So we need to have a way to tell in DT
> >>> which physical CPUs are connected to which CPU freq clock domain.
> >>>
> >>
> >> How about passing CPU freq clock domain id as along with phandle in
> >> qcom,freq-domain ?
> > 
> > Now sure what you mean here. There's no such this as CPUfreq clock 
> > domain id. It has policies that are made up of logical CPU numbers. 
> > Logical CPU is not something that you can fix in DT.
> > 
> > -Saravana
> 
> Sudeep,
> 
> Earlier the design was the freq_domain would take the CPU phandles
> 
> freq_domain:
>    cpus = <&cpu0 &cpu1....>;
> 

I believe Sudeep is recommending something I recommended earlier. It
would look like:

   cpu7 {
	   qcom,freq-domain = <&cpufreq_hw 1>;
   }

to indicate that cpu7 is in cpufreq_hw's frequency domain #1. That
should probably be called clk domain BTW.

If that was done with a phandle and a single cell, then we should have
something similar on the cpufreq_hw node side indicating how to parse
the cells in qcom,freq-domain. A property like #qcom,freq-domain-cells =
<1> to indicate that one u32 follows the phandle.