Re: [PATCH v2 0/4] iio: light: fix scale in veml6030

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 19 Jan 2025 18:31:57 +0100
Javier Carrasco <javier.carrasco.cruz@gmail.com> wrote:

> This series follows a similar approach as recently used for the veml3235
> by using iio-gts to manage the scale as stated in the ABI. In its
> current form, the driver exposes the hardware gain instead of the
> multiplier for the raw value to obtain a value in lux.
> 
> Although this driver and the veml3235 have many similarities, there are
> two main differences in this series compared to the one used to fix the
> other driver:
> 
> - The veml6030 has fractional gains, which are not supported by the
>   iio-gts helpers. My first attempt was adding support for them, but
>   that made the whole iio-gts implementation more complex, cumbersome,
>   and the risk of affecting existing clients was not negligible.
>   Instead, a x8 factor has been used for the hardware gain to present
>   the minimum value (x0.125) as x1, keeping linearity. The scales
>   iio-gts generates are therefore right without any extra conversion,
>   and they match the values provided in the different datasheets.
> 
> - This driver included a processed value for the ambient light, maybe
>   because the scale did not follow the ABI and the conversion was not
>   direct. To avoid breaking userspace, the functionality has been kept,
>   but of course using the fixed scales. In order to ease the
>   calculations, iio_gts_get_total_gain() has been exported to avoid
>   working directly with the scale in NANO, that would require 64-bit
>   operations.
> 
> To ease the usage of the iio-gts selectors, patches to support regfields
> and caching has been included.
> 
> This issue has been present since the original implementation, and it
> affects all devices it supports.
> 
> This series has been tested with a veml7700 (same gains as veml6030) and
> a veml6035 with positive results.
> 
> Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Whilst we might consider a backport eventually.  This is a huge patch
to do that with.  Hence I'll take this the slow way for next merge window.

For now I've applied patches 1 and 2 in the interest of nibbling away
at what we will need to see again ;)

Jonathan

> ---
> Changes in v2:
> - Rename SEL_GAIN to indicate they are in MILLI.
> - Split first patch (regfields and chaching).
> - Use regfield structs in chip struct instead of function pointer.
> - Use total gain to derive scale, avoiding 64-bit divisions.
> - Link to v1: https://lore.kernel.org/r/20250107-veml6030-scale-v1-0-1281e3ad012c@gmail.com
> 
> ---
> Javier Carrasco (4):
>       iio: light: veml6030: extend regmap to support regfields
>       iio: light: veml6030: extend regmap to support caching
>       iio: gts-helper: export iio_gts_get_total_gain()
>       iio: light: veml6030: fix scale to conform to ABI
> 
>  drivers/iio/industrialio-gts-helper.c |   3 +-
>  drivers/iio/light/Kconfig             |   1 +
>  drivers/iio/light/veml6030.c          | 608 +++++++++++++++++-----------------
>  include/linux/iio/iio-gts-helper.h    |   1 +
>  4 files changed, 299 insertions(+), 314 deletions(-)
> ---
> base-commit: 577a66e2e634f712384c57a98f504c44ea4b47da
> change-id: 20241231-veml6030-scale-8142f387e7e6
> 
> Best regards,