Re: [PATCHv6 0/4] thermal: add driver for R-Car Gen3

[Wolfram Sang <wsa@the-dreams.de>]

On Thu, Dec 22, 2016 at 11:38:19AM +0100, Niklas Söderlund wrote:
> Hi all,
> 
> The series adds thermal support to Renesas R-Car Gen3 SoCs. It's tested
> on Salvator-X H3 and M3-W SoC.
> 
> Wolfram asked me to have a look at the comments for v4 and to try and
> rework the temperature formulas to work with only ints and if it worked
> out resend the series. I have reworked code in 2/4 but kept Wolfram as
> the author and added my SoB, hope this is OK.
> 
> Reworking the formulas involved moving from s64 to int as the data type
> used to store coefficients used in binary scaled fixed point
> calculations. By examining the largest values which could be produced in
> these calculations a shift of 7 is the maximum scaling which is
> possible and still fit inside an int, previously with s64 the decimal scaling
> was 1000.
> 
> Changing the decimal scaling also reduces the accuracy of the
> calculations. In my tests this was hardly noticeable as the granularity
> of the reported temperature to user-space is 0.5C, comparing the value
> reported in the s64 vs int implementation only differ very slightly when
> it rounded the value to the next 0.5C level.
> 
> However the formulas used to calculate the coefficients are not
> documented and none obvious (at lest not to me) so given different
> initial values to calculate the coefficients the error might become
> larger. Therefore I would like to ask Morimoto-san and/or Khiem to
> provide or proxy testing of this less accurate formula and feedback if
> it's OK, let me know if there is anything I can do to help out.

Tested on H3 and M3-W. The temperatures I get when plugging the fan
on/off are very very similar to previous versions of this driver. Thus:

Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>