linux-kernel - [RFC PATCH 0/3] ad9832: driver cleanup

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Message-ID: <20251205202743.10530-1-tomasborquez13@gmail.com>
Date: Fri,  5 Dec 2025 17:27:40 -0300
From: Tomas Borquez <tomasborquez13@...il.com>
To: Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>,
	linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-staging@...ts.linux.dev,
	Tomas Borquez <tomasborquez13@...il.com>
Subject: [RFC PATCH 0/3] ad9832: driver cleanup

This series is a general cleanup of ad9832, with the purpose of 
graduating it from staging. The main changes are removing legacy 
platform_data support, converting to IIO channels with read/write_raw 
callbacks, and adding devicetree support.

I'm sending this as an RFC because I have some concerns about the ABI 
design and would appreciate guidance before putting more time into this.

Patch 1 removes the legacy platform_data support as suggested by
Jonathan [1]. The driver now initializes to a safe state and lets
userspace configure frequencies/phases via sysfs.

Patch 2 converts frequency and phase configuration from custom sysfs
attributes to proper IIO channels using read_raw/write_raw callbacks
(This is the main area where I'd like feedback).

Patch 3 adds devicetree bindings documentation.

Design Concerns:
1) Channel Organization and ABI Break

   The device has 2 frequency registers and 4 phase registers. Since both
   frequency and phase must use IIO_ALTVOLTAGE since there's no better fit
   (as far as I know), I've organized channels as:

     out_altvoltage0_frequency  (FREQ0)
     out_altvoltage1_frequency  (FREQ1)
     out_altvoltage2_phase      (PHASE0)
     out_altvoltage3_phase      (PHASE1)
     out_altvoltage4_phase      (PHASE2)
     out_altvoltage5_phase      (PHASE3)

   The old ABI used out_altvoltage0_frequency0, out_altvoltage0_frequency1,
   out_altvoltage0_phase0, etc. 

   The new approach felt cleaner but I'm open to alternatives and better 
   ways of mapping them. Is this channel mapping reasonable, or would a 
   different organization be preferred? And is the ABI break okay?

2) Scale Attributes

   The frequency scale is 1 Hz and phase scale is 2*PI/4096 radians.
   I cannot use info_mask_shared_by_type for IIO_CHAN_INFO_SCALE because
   all channels share IIO_ALTVOLTAGE.

   So instead I'm using IIO_CONST_ATTR for the scales:

     out_altvoltage_frequency_scale = "1"
     out_altvoltage_phase_scale = "0.0015339808"

   Is there a better approach here? Or should I just document the units and
   skip scale attributes entirely?

3) Remaining Custom Attributes

   Other controls remain as custom sysfs attributes:

     - out_altvoltage_frequencysymbol: select active frequency register
     - out_altvoltage_phasesymbol: select active phase register  
     - out_altvoltage_pincontrol_en: hardware pin control enable
     - out_altvoltage_out_enable: output enable

   I'm not sure if these map cleanly to IIO interfaces. Should these be
   documented in ABI or is there a preferred way to handle them?

4) Implementation Notes

   - read_raw uses explicit address switching rather than channel index
     arithmetic for clarity, though phase values could alternatively be
     accessed via st->phase[chan->channel - 2] and directly in freq with
     st->freq[chan->channel].
   - I'm unsure if mutex guards on cached reads are necessary.

Link: https://lore.kernel.org/linux-iio/20250628161040.3d21e2c4@jic23-huawei/ [1]
Signed-off-by: Tomas Borquez <tomasborquez13@...il.com>

Tomas Borquez (3):
  staging: iio: ad9832: remove platform_data support
  staging: iio: ad9832: convert to iio channels
  dt-bindings: iio: add analog devices ad9832/ad9835

 .../bindings/iio/frequency/adi,ad9832.yaml    |  65 +++++
 drivers/staging/iio/frequency/ad9832.c        | 264 +++++++++++-------
 drivers/staging/iio/frequency/ad9832.h        |  33 ---
 3 files changed, 233 insertions(+), 129 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/iio/frequency/adi,ad9832.yaml
 delete mode 100644 drivers/staging/iio/frequency/ad9832.h

-- 
2.43.0