Re: [PATCH v2 3/3] iio: magnetometer: st_magn: honour st,fullscale-milligauss DT property

[me@herrie.org]

On 2026-06-23 21:49, Andy Shevchenko wrote:
> On Tue, Jun 23, 2026 at 08:29:16PM +0100, Jonathan Cameron wrote:
>> On Tue, 16 Jun 2026 15:02:06 +0200
>> Herman van Hazendonk <github.com@herrie.org> wrote:
>> 
>> > The ST magnetometer core's common probe hardcodes fs_avl[0] -- the
>> > highest-sensitivity full-scale supported by the chip -- as the
>> > starting range. For the LSM303DLH that is +/-1.3 G; for the
>> > LSM303DLHC and LSM303DLM it is +/-2 G; for the LIS3MDL it is +/-4 G.
>> >
>> > That is the right default for "minimal noise floor at a desk", but
>> > it leaves no margin for boards that pick up appreciable DC bias from
>> > nearby PCB structures. On the HP TouchPad (apq8060 / tenderloin) the
>> > LSM303DLH magnetometer is mounted close enough to the surrounding
>> > power planes that X reads back as the chip's 0xF000 overflow
>> > sentinel (== -4096 raw, the value the chip publishes when the ADC
>> > saturates) on every sample at the chip-default range, while Y and Z
>> > fall well within the +/-1.3 G window.
>> >
>> > Parse the st,fullscale-milligauss device-tree property (documented
>> > separately in dt-bindings/iio/st,st-sensors.yaml) in the
>> > magnetometer common probe to select the initial fs_avl entry by its
>> > mg value. The DT binding pins the accepted value set per compatible
>> > via allOf/if-then enum clauses, so a malformed mg value fails
>> > dt_binding_check rather than reaching the driver. Sensors with a
>> > fixed full-scale (fs.addr == 0: LSM303AGR, LIS2MDL, IIS2MDC) have no
>> > register to switch and the property is rejected outright for them
>> > in the binding; the parse block is additionally gated on fs.addr as
>> > defence in depth against stale DTBs.
>> >
>> > Per-sensor mg ranges are listed in st_magn_sensors_settings[]. For
>> > LSM303DLH and LSM303DLHC/DLM the valid values are 1300, 1900, 2500,
>> > 4000, 4700, 5600 and 8100; for LIS3MDL, LSM9DS1-magn and LSM303C-magn
>> > they are 4000, 8000, 12000, 16000.
>> >
>> > Empirical scale sweep on the HP TouchPad confirmed that on this
>> > board any fs_avl >= 1 produces non-saturated X readings:
>> >
>> >     scale (0.001 G/LSB)  | X raw    Y raw    Z raw
>> >     --------------------+-------------------------------
>> >             1.100        | -4096    44       46    (X saturated)
>> >             0.855        |  -547    37       37    (clean)
>> >             0.670        |  -433    94      103    (clean)
>> >             0.450        |  -266    44       71    (clean)
>> >             0.400        |  -235    34       65    (clean)
>> >             0.330        |  -196    27       56    (clean)
>> >             0.230        |  -145    15       40    (clean)
>> >
>> > 2500 mg is the natural choice for tenderloin: comfortably outside
>> > the saturation regime while keeping useful precision for compass
>> > applications.
>> >
>> > Assisted-by: Claude:claude-opus-4-7 sparse smatch clang-analyzer coccinelle checkpatch
>> > Assisted-by: Sashiko:claude-opus-4-7
>> Hmm. First time I remember seeing Sashiko credited like this. Seems 
>> like pretty much
>> every patch series of any complexity would end up crediting sashiko.
>> Out of curiosity were you just looking at reports, or were you running 
>> it locally to
>> help with development?
> 
> I believe it's the second one, because LKML version uses Gemini (as far 
> as I
> understand the case). At least that's why I haven't commented on this 
> tag.
I have the whole toolchain running locally to avoid too many submissions 
and
feedback from Sashiko with Gemini after submitting. For small drivers I 
can run
Gemini locally as well, usually stick with Claude Opus 4.7 since that's 
what I
have a subscription for. For very complicated and large drivers Claude 
Opus
tends to time out even with 1 or 2 hour, so I fall back to Claude Haiku 
4.5
(which catches quite a few things, but is not as thorough as Opus or 
Gemini).

Seeing Sashiko tends to provide different feedback on different rounds, 
I try
to only submit when Sashiko and all others are clean.

Hope this clarifies!

Herman