Re: Device tree binding for DVFS table

On 07/11/2012 07:56 AM, Prashant Gaikwad wrote:

Hi,

I am working on DT binding for Tegra DVFS.

For Tegra, DVFS node mainly consists of frequency and voltage pairs.
Frequency in the pair may change for different process. E.g. for process
1 CPU clock frequency could be 900MHz at 1V while for process 2 it could
be 1GHz at 1V.
Tegra uses vendor specific ids to identify the correct frequency table.

Following is the proposed binding for voltage and frequency tables used
in DVFS. Looking for comments/suggestions to make it generic.

====DVFS table node=========> This node defines the voltage configuration for the DVFS which includes
the regulator and voltage array.

Required properties:

reg_id : <regulator phandle>;
voltage-table : <voltage array, values in mV>;

#address-cells and #size-cells : To identify correct frequency table
using process id (or some other vendor specific way).

====Frequency table node=======> 
This node defines frequency configuration for the device DVFS.

Required properties:

In device node need a reference to the DVFS table node.

dvfs : the phandle for the DVFS table node

frequency-table@n
       reg = <n>; dependent on address-cells and size-cells in DVFS
table node.
       frequencies = <frequency array, values in MHz>;

You are storing u32 values, why limit the resolution to MHz.

Put the unit in the property names.

}

Example:
-------------------------------------------------------------------------

cpu-dvfs-table : dvfs-table {

This should be located with the node that the frequencies correspond to.

              compatible = "nvidia,tegra30-dvfs-table";
              reg_id = <&sm0>;
              #address-cells = <1>;
              #size-cells = <0>;
              voltage-array = <750 775 800 825 850 875 900 925 950 975
1000 1025 1050 1100 1125>;

The SOC is really characterized at all these voltages?

};

device {
             dvfs = <&cpu-dvfs-table>;
             frequency-table@102 {
                      reg = <0x102>;
                      frequencies = <314 314 314 456 456 456 608 608 608
760 817 817 912 1000>;

I don't see the point of repeating frequencies.

             };
             frequency-table@002 {
                      reg = <0x002>;
                      frequencies = <598 598 750 750 893 893 1000>;
             };

How do you determine the voltage for a frequency on table 2?

I'd expect a single property with freq/volt pairs or 2 properties for
freq and voltage where there is a 1:1 relationship (freq N uses voltage N).

Rob

};

Thanks & Regards,
Prashant G

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