Re: Device tree binding for DVFS table

On Sun, Jul 15, 2012 at 4:42 PM, Rob Herring [off-list ref] wrote:

On 07/11/2012 11:08 PM, Prashant Gaikwad wrote:

quoted

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

quoted

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

quoted

quoted

quoted

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.

quoted

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>;

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

quoted

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.

quoted

Rob

quoted

};

Thanks&  Regards,
Prashant G

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel