Re: [PATCH v2 0/4] Add QST QMC5883P magnetometer driver

[Hardik Phalet <hardik.phalet@pm.me>]

On Fri Apr 10, 2026 at 10:06 AM IST, Andy Shevchenko wrote:
> On Thu, Apr 09, 2026 at 09:07:11PM +0000, Hardik Phalet wrote:
>> Verification steps performed:
>>   - Chip ID register (0x00) reads back 0x80 on probe, confirming the
>>     correct device is present
>>   - All three axes (in_magn_x_raw, in_magn_y_raw, in_magn_z_raw) return
>>     non-zero, stable values when the board is held still and change
>>     appropriately when the board is rotated
>>   - in_magn_x_scale (and Y, Z) returns the expected fractional value for
>>     the default ±8 G range (1/37500000)
>>   - in_magn_sampling_frequency / _available, in_magn_oversampling_ratio /
>>     _available, and downsampling_ratio / downsampling_ratio_available all
>>     read and write correctly; the chip responds without error to each
>>     valid setting
>>   - Runtime PM: after 2 s of inactivity the device enters suspend mode
>>     (MODE = 0x00 confirmed via i2cdump); the next sysfs read correctly
>>     resumes the device and returns valid data
>>   - System suspend/resume (echo mem > /sys/power/state) leaves the
>>     driver in a consistent state; readings remain valid after resume
>>   - dt_binding_check passes for patch 2/4
>>   - Kernel builds cleanly with W=1 and no new warnings
>
> This driver is rather huge. There are mistakes you made in the process, though:
> - never send a new version for such a code (amount and complexity) earlier than
> a week; give others a chance to review
Noted, Andy. I will take care of it from now on.

> - do not put driver to staging, why?
There are some functionality missing. But it has since been made clear
to me that that is not a valid reason. I will move to `drivers/iio`
in the next patch series.

> - the investigation is rather poor about existence of the driver — make sure
> there is no compatible (by register layout) driver in IIO or even outside it
> (for ADCs it might appear as HWMON [drivers/hwmon] or INPUT [drivers/input]
>  in some cases)
I will dig a bit deeper into this. But I could not find any thing
realted to the device I am working on (qmc5883p). 

There is a device hmc5843_core.c that already handles HMC5883L. But the
register layout is different, field ranges, gain encoding etc. are
different and I think warrants a separate driver. Other than that I
could not find something related to device I am working on. 

I will carefully go through HWMON and INPUT too, but do you have a
strategy to help me find somehting similar? It will be very useful.
Would `grep`-ing for 5883 and QST be a right starting point?

>
> --
> With Best Regards,
> Andy Shevchenko

Thank you for the review Andy, I appreciate your time!

Regards,
Hardik

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