Re: [PATCH] iio: gyro: mpu3050: restore cached sample rate on runtime resume

[Linus Walleij]

On Fri, Jun 5, 2026 at 10:47 AM Herman van Hazendonk
<github.com@xxxxxxxxxx> wrote:

> mpu3050_runtime_resume() only calls mpu3050_power_up(), which clears
> the SLEEP bit and waits 200 ms for the chip's register file to come
> back. It does not reprogram the full-scale, low-pass filter or sample
> rate divisor, all of which return to the chip's power-on defaults
> across a power cycle.
>
> The driver's cached state (mpu3050->fullscale, mpu3050->lpf,
> mpu3050->divisor) is the source of truth for what userspace observes
> through the IIO ABI: in_anglvel_sampling_frequency goes through
> mpu3050_get_freq() which reads the cached lpf and divisor, and
> in_anglvel_scale similarly reads cached fullscale. After the first
> autosuspend cycle the chip's actual sample rate diverges from what
> sysfs reports, until the next IIO_CHAN_INFO_RAW read incidentally
> reprograms the chip via mpu3050_set_8khz_samplerate() and the cached
> state restoration paths in mpu3050_fifo_read_one().
>
> That incidental restoration is only triggered by direct sysfs raw
> reads, not by buffered/triggered mode. A user who configures the
> sample rate, starts buffered capture and then leaves the device idle
> long enough to autosuspend will see chip-default-rate samples after
> resume rather than the configured rate.
>
> Reprogram the chip from the cached state in mpu3050_runtime_resume()
> by calling mpu3050_start_sampling() after mpu3050_power_up() succeeds.
> On failure power the chip back down to keep regulator and pm_runtime
> reference counts in sync with the error path.
>
> Fixes: 3904b28efb2c ("iio: gyro: Add driver for the MPU-3050 gyroscope")
> Signed-off-by: Herman van Hazendonk <github.com@xxxxxxxxxx>

Overall looks good to me, consider Andy's suggestion.
Reviewed-by: Linus Walleij <linusw@xxxxxxxxxx>

Yours,
Linus Walleij