Re: [PATCH v12 2/2] leds: Add driver for Qualcomm LPG

[Luca Weiss]

Hi Bjorn,

On Mittwoch, 16. Februar 2022 05:56:20 CET Bjorn Andersson wrote:
> The Light Pulse Generator (LPG) is a PWM-block found in a wide range of
> PMICs from Qualcomm. These PMICs typically comes with 1-8 LPG instances,
> with their output being routed to various other components, such as
> current sinks or GPIOs.
> 
> Each LPG instance can operate on fixed parameters or based on a shared
> lookup-table, altering the duty cycle over time. This provides the means
> for hardware assisted transitions of LED brightness.
> 
> A typical use case for the fixed parameter mode is to drive a PWM
> backlight control signal, the driver therefor allows each LPG instance
> to be exposed to the kernel either through the LED framework or the PWM
> framework.
> 
> A typical use case for the LED configuration is to drive RGB LEDs in
> smartphones etc, for which the driver supports multiple channels to be
> ganged up to a MULTICOLOR LED. In this configuration the pattern
> generators will be synchronized, to allow for multi-color patterns.
> 
> The idea of modelling this as a LED driver ontop of a PWM driver was
> considered, but setting the properties related to patterns does not fit
> in the PWM API. Similarly the idea of just duplicating the lower bits in
> a PWM and LED driver separately was considered, but this would not allow
> the PWM channels and LEDs to be configured on a per-board basis. The
> driver implements the more complex LED interface, and provides a PWM
> interface on the side of that, in the same driver.
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>

Works great on pm8941 / msm8974-fairphone-fp2!

Tested-by: Luca Weiss <luca@xxxxxxxxx>

Regards
Luca

> ---
> 
> Changes since v11:
> - Extended commit message to cover decision to put pwm_chip in the LED
> driver - Added Documentation, in particular for the hw_pattern format
> - Added a lock to synchronize requests from LED and PWM frameworks
> - Turned out that the 9bit selector differs per channel in some PMICs, so
>   replaced bitmask in lpg_data with lookup based on QPNP SUBTYPE
> - Fixed kerneldoc for the struct device pointer in struct lpg
> - Rewrote conditional in lut_free() to make it easier to read
> - Corrected and deduplicated max_period expression in lpg_calc_freq()
> - Extended nom/dom to numerator/denominator in lpg_calc_freq()
> - Replaced 1 << 9 with LPG_RESOLUTION in one more place in lpg_calc_freq()
> - Use FIELD_PREP() in lpg_apply_freq() as masks was introduced for reading
> the same in get_state()
> - Cleaned up the pattern format, to allow specifying both low and high pause
> with and without pingpong mode.
> - Only update frequency and pwm_value if PWM channel is enabled in
> lpg_pwm_apply - Make lpg_pwm_get_state() read the hardware state, in order
> to pick up e.g. bootloader backlight configuration
> - Use devm_bitmap_zalloc() to allocate the lut_bitmap
> - Use dev_err_probe() in lpg_probe()
> - Extended Kconfig help text to mention module name and satisfy checkpatch
> 
>  Documentation/leds/leds-qcom-lpg.rst |   76 ++
>  drivers/leds/Kconfig                 |    3 +
>  drivers/leds/Makefile                |    3 +
>  drivers/leds/rgb/Kconfig             |   18 +
>  drivers/leds/rgb/Makefile            |    3 +
>  drivers/leds/rgb/leds-qcom-lpg.c     | 1401 ++++++++++++++++++++++++++
>  6 files changed, 1504 insertions(+)
>  create mode 100644 Documentation/leds/leds-qcom-lpg.rst
>  create mode 100644 drivers/leds/rgb/Kconfig
>  create mode 100644 drivers/leds/rgb/Makefile
>  create mode 100644 drivers/leds/rgb/leds-qcom-lpg.c