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[2403:580d:82f4:0:d7db:fc6b:2721:a9be]) by smtp.gmail.com with ESMTPSA id ei56-20020a056a0080f800b00690c52267easm740206pfb.40.2023.10.31.01.21.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 Oct 2023 01:21:05 -0700 (PDT) Message-ID: <8ccd2d84-4422-4bc0-83a7-13a8c103e5e9@tweaklogic.com> Date: Tue, 31 Oct 2023 18:50:58 +1030 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] iio: light: Add support for APDS9306 Light Sensor Content-Language: en-US To: Matti Vaittinen , Jonathan Cameron Cc: Lars-Peter Clausen , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Andy Shevchenko , Paul Gazzillo , Matt Ranostay , Stefan Windfeldt-Prytz , linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20231027074545.6055-1-subhajit.ghosh@tweaklogic.com> <20231027074545.6055-3-subhajit.ghosh@tweaklogic.com> <20231028162025.4259f1cc@jic23-huawei> <84d7c283-e8e5-4c98-835c-fe3f6ff94f4b@gmail.com> <6a697c62-6a7c-4b31-bc8e-10f40db0363d@gmail.com> From: Subhajit Ghosh In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org On 31/10/23 17:41, Matti Vaittinen wrote: > 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 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. > > ... > >>>>> +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. > > ... > >> 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? > Hi Matti, Sorry, got busy with my full time job. It's nice to see that you have found the issue without my test results:) Please find below my tests - root@stm32mp1:/sys/bus/iio/devices/iio:device1# cat scale_available 14.009712000 4.669904000 2.334952000 1.751214000 1.556634666 0.875607000 0.778317333 0.583738000 0.437803500 0.291869000 0.218901750 0.194579333 0.145934500 0.109450875 0.097289666 0.072967250 0.048644833 0.036483625 0.024322416 0.018241812 0.012161208 0.006080604 root@stm32mp1:/sys/bus/iio/devices/iio:device1# echo 0.875607000 > scale ## This works root@stm32mp1:/sys/bus/iio/devices/iio:device1# echo 0.097289666 > scale ## This fails root@stm32mp1:/sys/bus/iio/devices/iio:device1# echo 0.097289667 > scale ## However if I add 1, it works! I figured, its a rounding issue so used this trick: "if (val2 % 10) val2 += 1;" I am sorry, I haven't gone through the full gts internals and only used your driver as a reference to understand it's implementation. I do not have any thoughts on top of my head now but let me go through the code. Regards, Subhajit Ghosh