Re: [PATCH v14 2/2] leds: Add driver for Qualcomm LPG

Doug Anderson
2022-03-03T22:11:02Z

Hi,

On Thu, Mar 3, 2022 at 1:41 PM Bjorn Andersson
<bjorn.andersson@linaro.org> 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@linaro.org>
> ---
>
> Changes since v13:
> - Fixed mixed space/tab indentation in documentation
> - Added 0 as to lpg_clk_rates[] to match the hardware state, to avoid + 1 in
> lpg_apply_freq() and - 1 in lpg_pwm_get_state()
> - Don't divide with 0 if current clock is 0 in lpg_pwm_get_state(), just return
> period = duty = 0 in this case
> - Renamed "clk" in struct lpg_channel to clk_sel
> - Renamed "pre_div" in struct lpg_channel to pre_div_sel
>
> Changes since v12:
> - Initialize ret in lpg_pwm_apply()
>
> 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 | 1405 ++++++++++++++++++++++++++
> 6 files changed, 1508 insertions(+)

Gets rid of the KASAN error and PWM still works for me, so happy to add back:

Tested-by: Douglas Anderson <dianders@chromium.org>

I haven't done a full review of the driver but I did a once-over of
the changes between v12 and v13 and they look good to me.

-Doug