Re: Device tree binding for DVFS table

[Prashant Gaikwad <pgaikwad@nvidia.com>]

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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>>
>