Messages in this thread | | | Date | Wed, 5 Aug 2015 12:20:39 +0200 | From | Sascha Hauer <> | Subject | Re: [PATCH 2/3] thermal: Add Mediatek thermal controller support |
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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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