Re: Device tree binding for DVFS table

Prashant Gaikwad <pgaikwad@xxxxxxxxxx> · Sat, 14 Jul 2012 00:00:14 +0530

Hi,

On Thursday 12 July 2012 09:38 AM, Prashant Gaikwad wrote:

On Wednesday 11 July 2012 07:33 PM, Rob Herring wrote:

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

Hi,

I am working on DT binding for Tegra DVFS.

<snip>

               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?

Not really, but different processes of single SoC are characterized 

for different voltages and this array covers all those 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).

How this will work:

voltage-array =<750 775 800 825 850 875 900  925 950 975 1000 1025 

1050 1100 1125>

frequencies-1 =<314 314 314 456 456 456 608  608 608 760 817  817  

912  1000>;

frequencies-2 =<598 598 750 750 893 893 1000>;

Freq and voltage has 1:1 relationship but as single voltage table is 

used for different processes we have more entries in voltage table 

than freq table.

Frequency table 1 is mapped till 1100mV while frequency table 2 is 

mapped till 900mV only, it maintains 1:1 relationship.

About repeating frequencies, operating voltage for a frequency would 

be the highest one mapped in the table.

For example, in frequency table 2 operating voltage for 750MHz would 

be 825mV while for 893MHz it would be 875mV. Unmapped entries could be 

replaced with 0 to make reading better.

Advantage it provides is single voltage table used for multiple 

frequency tables, as can be observed from above tables, operating 

voltage for 314MHz in freq table 1 is 800mV while there is no 

frequency in table 2 at that voltage.

I know this makes reading difficult but it provides flexibility,

I hope it explains the implementation.

Does this explanation help?

Regards,
Prashant G

Rob

};

Thanks&  Regards,
Prashant G

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