Re: [PATCH v2 5/6] iio: light: ROHM BU27034 Ambient Light Sensor

From: Matti Vaittinen
Date: Fri Mar 03 2023 - 04:18:01 EST

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In reply to: Andy Shevchenko: "Re: [PATCH v2 5/6] iio: light: ROHM BU27034 Ambient Light Sensor"
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Hi Andy,

Thanks again for the review. Some nice catches there.

On 3/2/23 17:34, Andy Shevchenko wrote:

On Thu, Mar 02, 2023 at 12:58:59PM +0200, Matti Vaittinen wrote:

ROHM BU27034 is an ambient light sesnor with 3 channels and 3 photo diodes
capable of detecting a very wide range of illuminance. Typical application
is adjusting LCD and backlight power of TVs and mobile phones.

Add initial support for the ROHM BU27034 ambient light sensor.

NOTE:
- Driver exposes 4 channels. One IIO_LIGHT channel providing the
calculated lux values based on measured data from diodes #0 and
#1. Additionally 3 IIO_INTENSITY channels are emitting the raw
register data from all diodes for more intense user-space
computations.
- Sensor has adjustible GAIN values ranging from 1x to 4096x.
- Sensor has adjustible measurement times 5, 55, 100, 200 and
400 mS. Driver does not support 5 mS which has special
limitations.
- Driver exposes standard 'scale' adjustment which is
implemented by:
1) Trying to adjust only the GAIN
2) If GAIN adjustment only can't provide requested
scale, adjusting both the time and the gain is
attempted.
- Driver exposes writable INT_TIME property which can be used
for adjusting the measurement time. Time adjustment will also
cause the driver to adjust the GAIN so that the overall scale
is not changed.
- Runtime PM is not implemented.
- Driver starts the measurement on the background when it is
probed. This improves the respnse time to read-requests
compared to starting the read only when data is requested.
When the most accurate 400 mS measurement time is used, data reads
would last quite long if measurement was started only on
demand. This, however, is not appealing for users who would
prefere power saving over measurement response time.

...

+config ROHM_BU27034
+ tristate "ROHM BU27034 ambient light sensor"

+ depends on I2C

How? I do not see a such.

I have assumed we need this because:

We select REGMAP_I2C which depends on I2C.
What happens if I2C=n and we select REGMAP_I2C? I may be wrong but I guess the I2C stays 'n' while REGMAP_I2C becomes y/m (?) I think that would be unfortunate - but I can't claim I am confident with how config dependencies are handled. I can drop this depends on if you're sure that's not a problem.

+ select REGMAP_I2C
+ select IIO_GTS_HELPER
+ help
+ Enable support for the ROHM BU27034 ambient light sensor. ROHM BU27034
+ is an ambient light sesnor with 3 channels and 3 photo diodes capable
+ of detecting a very wide range of illuminance.
+ Typical application is adjusting LCD and backlight power of TVs and
+ mobile phones.

Module name?

I am having a deja-vu.
https://lore.kernel.org/all/10c4663b-dd65-a545-786d-10aed6e6e5e9@xxxxxxxxxxxxxxxxx/

Module name is completely irrelevant when selecting a kernel configuration.

...

obj-$(CONFIG_OPT3001) += opt3001.o
obj-$(CONFIG_PA12203001) += pa12203001.o

+obj-$(CONFIG_ROHM_BU27034) += rohm-bu27034.o

If you see, most of the components are without vendor prefix, why rohm is
special? Like you are expecting the very same filename for something else?

No. I don't.

Using the vendor prefix in _file name_ was suggested to me by Lee already a few years ago. And I am actually grateful he did. I've found that _very_ useful as it simplifies finding the files I am looking for. What comes to the config option name, being able to easily search for the configs by vendor name has also been helpful.

...

+#include <linux/iio/iio.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/kfifo_buf.h>

Sorted?

Sure, thanks.

...

+#define BU27034_REG_DATA0_LO 0x50
+#define BU27034_REG_DATA1_LO 0x52
+#define BU27034_REG_DATA2_LO 0x54

I would drop _LO in all these

+#define BU27034_REG_DATA2_HI 0x55

and rename somehow this to something like _END / _MAX (similar to the fields.
Perhaps you would need _START / _MIN above.

I don't think this would improve anything. The _LO / _HI are descriptive as we have only two registers for each channel, _LO and _HI being more or less standard abbreviations for low and high.

...

+/*
+ * Available scales with gain 1x - 4096x, timings 55, 100, 200, 400 mS
+ * Time impacts to gain: 1x, 2x, 4x, 8x.
+ *
+ * => Max total gain is HWGAIN * gain by integration time (8 * 4096) = 32768
+ *
+ * Using NANO precision for scale we must use scale 64x corresponding gain 1x
+ * to avoid precision loss. (32x would result scale 976 562.5(nanos).
+ */
+#define BU27034_SCALE_1X 64
+
+#define BU27034_GSEL_1X 0x00
+#define BU27034_GSEL_4X 0x08
+#define BU27034_GSEL_16X 0x0a
+#define BU27034_GSEL_32X 0x0b
+#define BU27034_GSEL_64X 0x0c
+#define BU27034_GSEL_256X 0x18
+#define BU27034_GSEL_512X 0x19
+#define BU27034_GSEL_1024X 0x1a
+#define BU27034_GSEL_2048X 0x1b
+#define BU27034_GSEL_4096X 0x1c

Shouldn't the values be in plain decimal?

Why?

Otherwise I would like to understand bit mapping inside these hex values.

I like having register values in hex. It makes it obvious they don't necessarily directly match any 'real world' human-readable values.

...

+ .indexed = 1 \

+ Comma at the end.

ok.

...

+ static const int reg[] = {
+ [BU27034_CHAN_DATA0] = BU27034_REG_MODE_CONTROL2,
+ [BU27034_CHAN_DATA1] = BU27034_REG_MODE_CONTROL3,
+ [BU27034_CHAN_DATA2] = BU27034_REG_MODE_CONTROL2

Ditto.

ok.

+ };

...

+ struct bu27034_gain_check gains[3] = {
+ { .chan = BU27034_CHAN_DATA0, },
+ { .chan = BU27034_CHAN_DATA1, },

Inner commas are not needed.

+ { .chan = BU27034_CHAN_DATA2 }

But here the outer one is good to have.

+ };

...

+ if (chan == BU27034_CHAN_ALS) {
+ if (val == 0 && val2 == 1000)
+ return 0;
+ else

Redundant 'else'

Thanks for pointing out the unnecessary else. Killing it makes this nicer.

. And probably here is better to use standard pattern for
"checking for error first".

I prefer to check for this one specific exactly supported case for ALS channel. Cheking for 'all other possibilities but what we are expecting' would be counter intuitive.

+ return -EINVAL;
+ }

...

+ if (helper64 < 0xFFFFFFFFFFFFFLLU) {

Perhaps this needs a definition.

I like seeing the value here. It makes this less obfuscating. Comment makes the purpose obvious so adding a define would not really give any extra advantage.

+ helper64 *= gain0;
+ do_div(helper64, ch0);
+ } else {
+ do_div(helper64, ch0);
+ helper64 *= gain0;
+ }

+ /* Same overflow check here */

Why not a helper function?

I actually was thinking of it - but the check is smallish, only done twice and felt a tad too specific to warrant own function. I am not really against adding a function if you feel strongly about this :)

+ if (helper64 < 0xFFFFFFFFFFFFFLLU) {
+ helper64 *= gain0;
+ do_div(helper64, helper);
+ } else {
+ do_div(helper64, helper);
+ helper64 *= gain0;
+ }

...

+ return (val & BU27034_MASK_VALID);

Unneeded parentheses.

ok.

...

+retry:
+ /* Get new value from sensor if data is ready */
+ if (bu27034_has_valid_sample(data)) {
+ ret = regmap_bulk_read(data->regmap, BU27034_REG_DATA0_LO,
+ res, size);
+ if (ret)
+ return ret;
+
+ bu27034_invalidate_read_data(data);
+ } else {
+ /* No new data in sensor. Wait and retry */
+ msleep(25);
+
+ goto retry;

There is no way out. What might go wrong?

Beyond hanging the user process? :)

I think you have a point here. I'll add a timeout.

+ }

...

+ ret = bu27034_get_int_time(data);

_get_int_time_us() ? (Looking at the below code)

+ if (ret < 0)
+ return ret;
+
+ msleep(ret / 1000);

...

+ * Avoid div by zeroi. Not using max() as the data may not be in

zeroi?

...

+ if (!res[0])

Positive conditional?

No. Again, we check for the very specific case where res has all bits zeroed. Inverse condition is counter intuitive.

+ ch0 = 1;
+ else
+ ch0 = le16_to_cpu(res[0]);
+
+ if (!res[1])
+ ch1 = 1;

Ditto.

+ else
+ ch1 = le16_to_cpu(res[1]);

But why not to read and convert first and then check.

Because conversion is not needed if channel data is zero.

This at least will
correctly compare 0 to the LE16 0 (yes, it's the same for 0, but strictly
speaking the bits order of lvalue and rvalue is different).

and hence we check for !res[0]

...

+ switch (mask) {
+ case IIO_CHAN_INFO_INT_TIME:
+ return iio_gts_avail_times(&data->gts, vals, type, length);
+ case IIO_CHAN_INFO_SCALE:
+ return iio_gts_all_avail_scales(&data->gts, vals, type, length);
+ default:
+ break;
+ }
+
+ return -EINVAL;

You may do it from default case.

I think we have discussed this one in the past too. I like having return at the end of a non void function.

...

+ ret = regmap_read_poll_timeout(data->regmap, BU27034_REG_MODE_CONTROL4,
+ val, (val & BU27034_MASK_VALID),

Redundant parentheses.

+ BU27034_DATA_WAIT_TIME_US,
+ BU27034_TOTAL_DATA_WAIT_TIME_US);
+ if (ret) {
+ dev_err(data->dev, "data polling %s\n",
+ !(val & BU27034_MASK_VALID) ? "timeout" : "fail");

Why not positive conditional in ternary?

Because I check this for a specific case: "Was it a timeout?" - not for unspecified "Was it something else but timeout?"

+ return ret;
+ }

...

+ fwnode = dev_fwnode(dev);
+ if (!fwnode)
+ return -ENODEV;

So, you deliberately disable a possibility to instantiate this from user space,
why?

Thanks! (And Sorry. Jonathan pointed this out to me already in the RFC.) I thought I already fixed this.

...

+ ret = devm_iio_kfifo_buffer_setup(dev, idev, &bu27034_buffer_ops);
+
+ ret = devm_iio_device_register(dev, idev);

Don't you find something strange in between?

Thanks!

+ if (ret < 0)
+ return dev_err_probe(dev, ret,
+ "Unable to register iio device\n");

...

+ { .compatible = "rohm,bu27034", },

Inner comma is not needed.

ok

--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~

Next message: Varadarajan Narayanan: "Re: [PATCH 4/8] clk: qcom: gcc-ipq9574: Add USB related clocks"
Previous message: Dmitry Rokosov: "Re: [PATCH v9 5/5] dt-bindings: clock: meson: add A1 Peripherals clock controller bindings"
In reply to: Andy Shevchenko: "Re: [PATCH v2 5/6] iio: light: ROHM BU27034 Ambient Light Sensor"
Next in thread: Jonathan Cameron: "Re: [PATCH v2 5/6] iio: light: ROHM BU27034 Ambient Light Sensor"
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