Messages in this thread | | | Date | Tue, 31 Oct 2023 09:11:37 +0200 | Subject | Re: [PATCH v2 2/2] iio: light: Add support for APDS9306 Light Sensor | From | Matti Vaittinen <> |
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On 10/30/23 12:21, Matti Vaittinen wrote: > Hi dee Ho peeps, > > On 10/29/23 17:51, Matti Vaittinen wrote: >> On 10/28/23 18:20, Jonathan Cameron wrote: >>> On Fri, 27 Oct 2023 18:15:45 +1030 >>> Subhajit Ghosh <subhajit.ghosh@tweaklogic.com> wrote: >>> >>>> Driver support for Avago (Broadcom) APDS9306 Ambient Light Sensor >>>> with als >>>> and clear channels with i2c interface. Hardware interrupt >>>> configuration is >>>> optional. It is a low power device with 20 bit resolution and has >>>> configurable adaptive interrupt mode and interrupt persistence mode. >>>> The device also features inbuilt hardware gain, multiple integration >>>> time >>>> selection options and sampling frequency selection options.
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>>>> +static int apds9306_scale_set(struct apds9306_data *data, int val, >>>> int val2) >>>> +{ >>>> + int i, ret, time_sel, gain_sel; >>>> + >>>> + /* Rounding up the last digit by one, otherwise matching table >>>> fails! */ >>> >>> Interesting. Sounds like a question for Matti? >> >> Sounds odd indeed. I assume this happens when scale setting is >> requested using one of the exact values advertised by the available >> scales from the GTS? This does not feel right and the +1 does not ring >> a bell to me. I need to investigate what's going on. It would help if >> you could provide the values used as val and val2 for the setting. >> >> This will take a while from me though - I'll try to get to this next >> week. Thanks for pointing out the anomaly! >> > > I think I have a rough understanding. I did a Kunit test which goes > through all the available scales values from the > gts->avail_all_scales_table and all integration times, and feeds them to > the logic below. It seems the first culprit is hit by: > val = 0, val2 = 125025502. > > Problem is that the 125025502 is rounded. The exact linearized NANO > scale resulting from time multiplier 128, gain multiplier 1 is > 125025502.5 - which means we will see rounding. > >>> >>>> + if (val2 % 10) >>>> + val2 += 1; > > For a while I was unsure if this check works for all cases because I see > linearized scales: > 250051005 - multipliers 1x, 64x > 83350335 - multipliers 3x, 64x and 6x, 32x > 27783445 - multipliers 9x, 64x. > > For those we will get + 1 added to val2 even though there is no > rounding. It appears this is not a problem because the > iio_gts_get_gain() (which is used to figure out the required total gain > to get the desired scale) does not require the scale to be formed by > exact multiples of gain.
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> I think it would be very nice if the gts-helpers could do the rounding > when computing the available scales, but that'd require some thinking. > Fixup patch is still very welcome ;)
I did some further experimenting. Basically, I did a "hack" which always rounds up the available-scales values if division results a remainder. This way the values advertised by the available_scales did find the matching table.
It is a tiny bit icky because for example the scale 6945861.25 becomes 6945862 in available-scales. Also, I assume that if we "hack" just the available-scales and don't fix the rest of the logic, setting 6945862 will read back as 6945861 (I haven't tested this though). Also, the 20837583.75 will be 20837583 in available-scales but 20837582 when read back, resulting small error. (I haven't tested this either but I assume the current GTS code is flooring the 20837583.75 to 20837583.
I am wondering if changing the iio_gts_get_gain() to do rounding instead of flooring and changing also the iio_gts_total_gain_to_scale() to something like:
int iio_gts_total_gain_to_scale(struct iio_gts *gts, int total_gain, int *scale_int, int *scale_nano) { u64 tmp; int rem;
tmp = gts->max_scale;
rem = do_div(tmp, total_gain); if (total_gain > 1 && rem >= total_gain / 2) tmp += 1ULL;
return iio_gts_delinearize(tmp, NANO, scale_int, scale_nano); }
would do the trick. It's just that I'm a bit afraid of touching the iio_gts_get_gain() - by the very least I need to fire up the GTS tests which I implemented but are not in-tree due to the test-device dependency... :/
Any thoughts?
>>>> + >>>> + ret = iio_gts_find_gain_sel_for_scale_using_time(&data->gts, >>>> + data->intg_time_idx, val, val2, &gain_sel); >>>> + if (ret) { >>>> + for (i = 0; i < data->gts.num_itime; i++) { >>>> + time_sel = data->gts.itime_table[i].sel; >>>> + >>>> + if (time_sel == data->intg_time_idx) >>>> + continue; >>>> + >>>> + ret = >>>> iio_gts_find_gain_sel_for_scale_using_time(&data->gts, >>>> + time_sel, val, val2, &gain_sel); >>>> + if (!ret) >>>> + break; >>>> + } >>>> + if (ret) >>>> + return -EINVAL; >>>> + >>>> + ret = apds9306_intg_time_set_hw(data, time_sel); >>>> + if (ret) >>>> + return ret; >>>> + } >>>> + >>>> + return apds9306_gain_set_hw(data, gain_sel); >>>> +}
Yours, -- Matti
-- Matti Vaittinen Linux kernel developer at ROHM Semiconductors Oulu Finland
~~ When things go utterly wrong vim users can always type :help! ~~
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