Device tree binding for DVFS table

[Turquette, Mike]

On Sun, Jul 15, 2012 at 4:42 PM, Rob Herring <robherring2 at gmail.com> wrote:
> On 07/11/2012 11:08 PM, Prashant Gaikwad wrote:
>> On Wednesday 11 July 2012 07:33 PM, Rob Herring wrote:
>>> On 07/11/2012 07:56 AM, Prashant Gaikwad wrote:
>
>>>> cpu-dvfs-table : dvfs-table {
>>> This should be located with the node that the frequencies correspond to.
>>>
>>
>> With CAR node?
>
> With the power domain it corresponds to or the cpu nodes.
>
>>
>>>>                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 at 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 at 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>;
>>
>
> I don't see the point trying to share a voltage range. Not sharing it is
> fewer array elements (22 vs 36):
>
> voltage-array-1 =<750 825 900 975 1000 1050 1100>;
> frequencies-1   =<314 456 608 760  817  912 1000>;
>
> voltage-array-2 =<750 800 850  900>
> frequencies-2   =<598 750 893 1000>;
>

This is significantly more readable.

Regards,
Mike

> Rob
>
>>
>> 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.
>>
>>> Rob
>>>
>>>> };
>>>>
>>>> Thanks&  Regards,
>>>> Prashant G
>>>>
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>>>
>>
>
>