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

[Doug Anderson <dianders@chromium.org>]

Hi Pavel,

On Thu, Mar 3, 2022 at 2:10 PM Doug Anderson <dianders@chromium.org> wrote:
>
> 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.

With v5.18-rc1 released, this seems like it would be an ideal time to
land this driver and its bindings in a for-next branch for the leds
subsystem. Is there anything blocking it? Are you the right person to
land them? Ideally the bindings / driver (patch #1 and #2) from
Satya's series [1] could land right atop it since it's ready too?

[1] https://lore.kernel.org/r/1645509309-16142-1-git-send-email-quic_c_skakit@quicinc.com/

Thanks!

-Doug