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.
>
> But we definately need something to test on to do this right>
> Yours,
> Linus Walleij
>
Thanks,
Jonathan Bakker
