Re: [PATCH v13 5/6] iio: adc: ad4691: add oversampling support

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 25 May 2026 13:10:14 +0300
Radu Sabau via B4 Relay <devnull+radu.sabau.analog.com@kernel.org> wrote:

> From: Radu Sabau <radu.sabau@analog.com>
> 
> Add per-channel oversampling ratio (OSR) support for CNV burst mode.
> The accumulator depth register (ACC_DEPTH_IN) is programmed with the
> selected OSR at buffer enable time and before each single-shot read.
> 
> Supported OSR values: 1, 2, 4, 8, 16, 32.
> 
> Introduce AD4691_MANUAL_CHANNEL() for manual mode channels, which do
> not expose the oversampling_ratio attribute since OSR is not applicable
> in that mode. A separate manual_channels array is added to
> struct ad4691_channel_info and selected at probe time.
> 
> in_voltageN_sampling_frequency represents the effective output rate for
> channel N, defined as osc_freq / osr[N]. The chip has one internal
> oscillator shared by all channels; each channel independently
> accumulates osr[N] oscillator cycles before producing a result.

Sashiko notes this probably needs updating for moving to single osr.

> 
> Writing sampling_frequency computes needed_osc = freq * osr[N] and
> snaps down to the largest oscillator table entry that satisfies both
> osc <= needed_osc and osc % osr[N] == 0, guaranteeing an exact integer
> read-back. The result is stored in target_osc_freq_Hz and written to
> OSC_FREQ_REG at buffer enable and single-shot time, so sampling_frequency
> and oversampling_ratio can be set in any order.
> 
> in_voltageN_sampling_frequency_available is precomputed at probe for
> each OSR value, listing only oscillator table entries that divide
> evenly by that OSR, expressed as effective rates (osc_freq / osr[N]).
> The list becomes sparser as OSR increases, capping at max_rate / osr[N].
> read_avail picks the precomputed list for the channel's current OSR,
> making the returned pointer stable and race-free.
> 
> Writing oversampling_ratio stores the new OSR for that channel and snaps
> target_osc_freq_Hz to the largest oscillator table entry that is both
> <= old_effective_rate * new_osr and evenly divisible by new_osr. This
> preserves an integer read-back of in_voltageN_sampling_frequency after
> the OSR change while keeping the oscillator as close as possible to the
> previous effective rate.
> 
> OSR defaults to 1 (no accumulation) for all channels.
> 
> Signed-off-by: Radu Sabau <radu.sabau@analog.com>
I didn't find anything else to comment on. LGTM

Thanks,

Jonathan