[v3,0/2] iio: light: fix scale in veml6030

Message

Javier Carrasco Jan. 27, 2025, 7:30 p.m. UTC

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.

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 <[e-mail]>
---
Changes in v3:
- Rebase onto iio/testing and drop [1/4], [2/4] (applied).
- iio-gts: document exported function.
- Link to v2: https://lore.kernel.org/r/[e-mail]

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/[e-mail]

---
Javier Carrasco (2):
      iio: gts-helper: export iio_gts_get_total_gain()
      iio: light: veml6030: fix scale to conform to ABI

 drivers/iio/industrialio-gts-helper.c |  11 +-
 drivers/iio/light/Kconfig             |   1 +
 drivers/iio/light/veml6030.c          | 528 ++++++++++++++--------------------
 include/linux/iio/iio-gts-helper.h    |   1 +
 4 files changed, 229 insertions(+), 312 deletions(-)
---
base-commit: ed2010907caa1c838d2e565d67bbc08fe023663e
change-id: 20241231-veml6030-scale-8142f387e7e6

Best regards,

Comments

Jonathan Cameron Jan. 28, 2025, 7:13 p.m. UTC | #1

On Mon, 27 Jan 2025 20:30:21 +0100
Javier Carrasco <[e-mail]> 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.
> 
> 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 <[e-mail]>
Applied to the togreg branch of iio.git. Initially pushed out as testing.

I've rebased on char-misc, but will almost certainly rebase once more on rc1
once available.

> ---
> Changes in v3:
> - Rebase onto iio/testing and drop [1/4], [2/4] (applied).
> - iio-gts: document exported function.
> - Link to v2: https://lore.kernel.org/r/[e-mail]
> 
> 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/[e-mail]
> 
> ---
> Javier Carrasco (2):
>       iio: gts-helper: export iio_gts_get_total_gain()
>       iio: light: veml6030: fix scale to conform to ABI
> 
>  drivers/iio/industrialio-gts-helper.c |  11 +-
>  drivers/iio/light/Kconfig             |   1 +
>  drivers/iio/light/veml6030.c          | 528 ++++++++++++++--------------------
>  include/linux/iio/iio-gts-helper.h    |   1 +
>  4 files changed, 229 insertions(+), 312 deletions(-)
> ---
> base-commit: ed2010907caa1c838d2e565d67bbc08fe023663e
> change-id: 20241231-veml6030-scale-8142f387e7e6
> 
> Best regards,