On Sun, 26 Jan 2020 20:27:22 +0000 Jonathan Bakker <xc-racer2@xxxxxxx> wrote: > Hi Linus, > > On 2020-01-26 7:16 a.m., Linus Walleij wrote: > > On Fri, Jan 24, 2020 at 1:47 AM Jonathan Bakker <xc-racer2@xxxxxxx> wrote: > > > >> Thanks for the driver, I've tested it on a first-gen Galaxy S > >> device with a GP2AP002A00F. I have a few comments that I've put inline > >> based on my experiences. > > > > Thanks a lot! > > > >> Both shortly after probe (when runtime pm timeout occurs?) and after > >> manually disabling the proximity event, this > >> irq handler is called. Since the chip is in low power state, it obviously > >> fails to read the proximity value and write to the OCON register below, eg > >> > >> [ 7.215875] gp2ap002 11-0044: error reading proximity > >> [ 8.105878] gp2ap002 11-0044: error setting up VOUT control 1 > >> > >> Can we do something like disable_irq() in the runtime pm function to prevent > >> this? > > > > I added that in v6, I hope this solves your problem. > > Yep, it appears to. Thanks. > > > > >> The gp2ap002s00f_regmap_i2c_read function works on the gp2ap002a00f as well, > >> so this can be simplified/dropped. > > > > Fixed this too in v6. > > > >>> + if (ch_type != IIO_CURRENT) { > >>> + dev_err(dev, > >>> + "wrong type of IIO channel specified for ALSOUT\n"); > >>> + return -EINVAL; > >>> + } > >> > >> This enforces a current ADC, while several devices besides mine (eg Galaxy Nexus) > >> use a resistor and a voltage ADC. For this case, could we add a device property such as > >> sharp,adc-adjustment-ratio to convert from the raw ADC values to a "current" that > >> could be used in the lookup table? So the "current" would be the raw ADC divided > >> by that special value. > >> > >> Instructions for converting the ADC back to the current can be found eg at > >> https://android.googlesource.com/device/samsung/crespo/+/2e0ab7265e3039fee787c2216e0c98d92ea0b49e%5E%21/#F0 > > > > I'd like to keep that as a future enhancement unless someone is very eager > > to get it and has a device they can test it on. Otherwise it will be > > just dry-coding > > on my part. > > Well, I've got such a device and can test :) > > > > > I think the property we would add in the device tree in that case should > > be the resistance value. This is based on the following assumption > > which is indeed a bit of speculation since there is no proper datasheet > > for the light sensor part of the component: > > > > - The light sensor part is simply a photodiode > > - This emits a nonlinear current in relation to how many > > photons hit the photodiode in a time interval, the relationship > > is described in the curren->lux table we have > > - Some vendors do not have any current ADC, so they connect > > this to a resistor, and measure the voltage over the > > resistor because the have a voltage ADC > > > > Since current is linear to the voltage over the resistor, we should > > include the resistance in the device tree, then using that the > > corresponding current can be calculated and we use the same > > look-up table to find the lux. Probably each system may need > > to also subtract some bias voltage or so. > > Yes, this is my understanding of it as well (I also have no datasheet). > > Given V = actual voltage in V, Vref = reference voltage of ADC in V, ADC = value > read from ADC, ADCmax = maximum possible value read from ADC, I = current in amps, > R = resistor value in ohms, uA = current in microamps > > V / Vref = ADC / ADCmax > V = (ADC / ADCmax) * Vref > > V = I * R > I * R = (ADC / ADCmax) * Vref > I = ADC * Vref / ADCmax / R > > However, because we want the current in uA for the table, (note, your comment says > that the table is based on mA, but I believe that it should actually be uA) > > uA = ADC * Vref / ADCmax / R * 1000000 > > Then, in order to avoid multiplying by a decimal, the uA is the ADC value divided > by the inverse of > > (1000000 * Vref / ADCmax / R) > > For example, on the first gen Galaxy S series and the Nexus S, the Vref is 3.3V, > the ADC is 12 bit (2^12 = 4096, so high value is 4095), the resistor is 47000ohms, > > inverse of (1000000 * 3.3 / 4095 / 47000) = 58 > > so we need to divide the raw ADC reading by 58 in order to get the uA for the current->lux > table. > > A quick patch that I used for testing (based off of v5) is > > diff --git a/drivers/iio/light/gp2ap002.c b/drivers/iio/light/gp2ap002.c > index a5897959f70d..b98aec337f8b 100644 > --- a/drivers/iio/light/gp2ap002.c > +++ b/drivers/iio/light/gp2ap002.c > @@ -130,6 +130,7 @@ > * @vdd: regulator controlling VDD > * @vio: regulator controlling VIO > * @alsout: IIO ADC channel to convert the ALSOUT signal > + * @adc_adj: conversion factor if voltage ADC used instead of current ADC > * @is_gp2ap002s00f: this is the GP2AP002F variant of the chip > * @enabled: we cannot read the status of the hardware so we need to > * keep track of whether the event is enabled using this state variable > @@ -143,6 +144,7 @@ struct gp2ap002 { > enum iio_event_direction dir; > u8 hys_far; > u8 hys_close; > + u8 adc_adj; > bool is_gp2ap002s00f; > bool enabled; > }; > @@ -272,6 +274,9 @@ static int gp2ap002_get_lux(struct gp2ap002 *gp2ap002) > if (ret < 0) > return ret; > > + if (gp2ap002->adc_adj) > + res /= gp2ap002->adc_adj; > + > dev_dbg(gp2ap002->dev, "read %d mA from ADC\n", res); > > ill1 = &gp2ap002_illuminance_table[0]; > @@ -588,7 +593,16 @@ static int gp2ap002_probe(struct i2c_client *client, > ret = iio_get_channel_type(gp2ap002->alsout, &ch_type); > if (ret < 0) > return ret; > - if (ch_type != IIO_CURRENT) { > + if (ch_type == IIO_VOLTAGE) { > + ret = device_property_read_u8(dev, > + "sharp,adc-adjustment-ratio", &val); > + if (ret) { > + dev_err(dev, > + "failed to obtain adc conversion\n"); > + return -EINVAL; > + } > + gp2ap002->adc_adj = val; > + } else if (ch_type != IIO_CURRENT) { > dev_err(dev, > "wrong type of IIO channel specified for ALSOUT\n"); > return -EINVAL; > > Alternatively, you could collect the resistor value, the ADC precision (this doesn't > appear to be queryable via the IIO layer), and the reference voltage level - but I'm > not sure how you'd do the inverse calculation in the kernel. An alternative to doing this is to represent the resistor circuit explicitly. You end up with a really small ADC driver that is a consumer of a voltage and provides a current channel. That has all the properties of the circuit via DT. We do some stuff a bit similar to this in the envelope detector driver. In general I would prefer we handle this sort of conversion generically rather than bolting it into a light sensor driver like you are doing here, even if it comes at the cost of a bit more complexity. Jonathan > > > > > But we definately need something to test on to do this right> > > Yours, > > Linus Walleij > > > > Thanks, > Jonathan Bakker