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

[David Lechner]

On 4/9/26 4:07 PM, Hardik Phalet wrote:

For a series this be, please wait at least a week for more feedback
before submitting the next revision.

> This series adds initial Linux support for the QST QMC5883P, a 3-axis
> anisotropic magneto-resistive (AMR) magnetometer with a 16-bit ADC that
> communicates over I2C. To my knowledge there is no existing upstream
> driver for this device.
> 
> The driver supports:
>   - Raw magnetic field readings on X, Y, and Z axes
>   - Four selectable full-scale ranges (±2 G, ±8 G, ±12 G, ±30 G)
>   - Configurable output data rate (10, 50, 100, 200 Hz)
>   - Configurable oversampling ratio (1, 2, 4, 8)
>   - Configurable downsampling ratio (1, 2, 4, 8) via a custom sysfs

What is the difference between oversampling and downsampling? I think
we have used some filter attribute for downsampling/decimation in some
other drivers so maybe that could be a good fit?

>     attribute
>   - Runtime PM with a 2 s autosuspend delay
>   - System suspend/resume via pm_runtime_force_suspend/resume
> 
> Regmap with an rbtree cache is used throughout. CTRL_1 and CTRL_2
> bit fields are accessed via regmap_field to avoid read-modify-write
> races. The STATUS register is marked precious so regmap never reads
> it speculatively and clears the DRDY/OVFL bits unexpectedly.
> 
> The init sequence on probe is: soft reset → wait 1 ms → deassert
> reset → configure SET/RESET control → apply default ODR/OSR/DSR/RNG
> → enter normal mode. This ordering was determined empirically on
> hardware to produce reliable, non-zero axis readings.
> 
> The driver is placed under drivers/staging/iio/magnetometer/ with a
> TODO file tracking the remaining work before it can graduate:
>   - Triggered buffer support (iio_triggered_buffer_setup)
>   - DRDY interrupt support
>   - Self-test implementation

These are not reasons to have the driver in staging. It is fine
to have a driver that doesn't implement all functionality. We should
be able to add those features without breaking anything.