Re: Device tree binding for DVFS table

Hi,

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

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

quoted

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

quoted

Hi,

I am working on DT binding for Tegra DVFS.

<snip>

quoted

quoted

               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.

quoted

quoted

};

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.

quoted

              };
              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

quoted

Rob

quoted

};

Thanks&  Regards,
Prashant G

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