Re: [PATCH 2/3] thermal: Add Mediatek thermal controller support

Sascha Hauer
2015-08-05T10:20:51Z

On Tue, Jul 21, 2015 at 11:13:22PM +0800, Daniel Kurtz wrote:
> Hi Sascha,
>
> Review comments inline...
>
> > + *
> > + * This converts the raw ADC value to mcelsius using the SoC specific
> > + * calibration constants
> > + */
> > +static int raw_to_mcelsius(struct mtk_thermal *mt, u32 raw)
> > +{
> > + s32 format_1, format_2, format_3, format_4;
>
> The formula would be easier to follow with better variable names than
> "format_X".
>
> > + s32 xtoomt;
>
> What does "xtoomt" mean?
>
> > + s32 gain;
> > +
> > + raw &= 0xfff;
> > +
> > + gain = (10000 + mt->adc_ge);
>
> no outer ()
>
> > +
> > + xtoomt = ((((mt->vts + 3350 - mt->adc_oe) * 10000) / 4096) * 10000) /
> > + gain;
> > +
> > + format_1 = ((mt->degc_cali * 10) >> 1);
>
> When doing computations, I think "A / 2" is preferred over "A >> 1".
> Also, no outer ().
>
> > + format_2 = (raw - mt->adc_oe);
> > + format_3 = (((((format_2) * 10000) >> 12) * 10000) / gain) - xtoomt;
>
> This is just:
> format_3 = ((((raw - mt->vts - 3350) * 10000) / 4096) * 10000) / gain;
>
> No wonder mt->adc_oe = 512-512 = 0... it just cancels itself out here, anyway.
>
> > + format_3 = format_3 * 15 / 18;
>
> Of course we should multiply by 15/18!
> What is going on here? Why this magic 5/6 ratio?
>
> > + format_4 = ((format_3 * 100) / (165 + mt->o_slope));
>
> no outer ()
>
> > + format_4 = format_4 - (format_4 << 1);
>
> Hmm...
> A = X - 2*X;
> otherwise known as:
> A = -X;
>
> > + return (format_1 + format_4) * 100;
>
> Or just:
> return (format_1 - format_4) * 100;

I must admit I took this calculation from the original driver and never
looked at it. Simplifying this further this goes down to:

static int raw_to_mcelsius(struct mtk_thermal *mt, u32 raw)
{
return mt->calib_b + mt->calib_a * (raw & 0xfff);
}

with calib_a = -123 and calib_b = 465124.

I'll address this and the other comments in v2.

Sascha

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