Message-ID: <20220224165939.4275x7mzp7qpl2kj@pengutronix.de>
Date:   Thu, 24 Feb 2022 17:59:39 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Pavel Machek <pavel@....cz>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jonathan Corbet <corbet@....net>, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, Luca Weiss <luca@...tu.xyz>,
        Doug Anderson <dianders@...omium.org>
Subject: Re: [PATCH v13 2/2] leds: Add driver for Qualcomm LPG

On Fri, Feb 18, 2022 at 10:31:16AM -0800, 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.
> 
> Tested-by: Luca Weiss <luca@...tu.xyz>
> Tested-by: Doug Anderson <dianders@...omium.org>
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
> 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     | 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
> 
> diff --git a/Documentation/leds/leds-qcom-lpg.rst b/Documentation/leds/leds-qcom-lpg.rst
> new file mode 100644
> index 000000000000..d4825a289888
> --- /dev/null
> +++ b/Documentation/leds/leds-qcom-lpg.rst
> @@ -0,0 +1,76 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +==============================
> +Kernel driver for Qualcomm LPG
> +==============================
> +
> +Description
> +-----------
> +
> +The Qualcomm LPG can be found in a variety of Qualcomm PMICs and consists of a
> +number of PWM channels, a programmable pattern lookup table and a RGB LED
> +current sink.
> +
> +To facilitate the various use cases, the LPG channels can be exposed as
> +individual LEDs, grouped together as RGB LEDs or otherwise be accessed as PWM
> +channels. The output of each PWM channel is routed to other hardware
> +blocks, such as the RGB current sink, GPIO pins etc.
> +
> +The each PWM channel can operate with a period between 27us and 384 seconds and
> +has a 9 bit resolution of the duty cycle.
> +
> +In order to provide support for status notifications with the CPU subsystem in
> +deeper idle states the LPG provides pattern support. This consists of a shared
> +lookup table of brightness values and per channel properties to select the
> +range within the table to use, the rate and if the pattern should repeat.
> +
> +The pattern for a channel can be programmed using the "pattern" trigger, using
> +the hw_pattern attribute.
> +
> +/sys/class/leds/<led>/hw_pattern
> +--------------------------------
> +
> +Specify a hardware pattern for a Qualcomm LPG LED.
> +
> +The pattern is a series of brightness and hold-time pairs, with the hold-time
> +expressed in milliseconds. The hold time is a property of the pattern and must
> +therefor be identical for each element in the pattern (except for the pauses
> +described below).
> +
> +Simple pattern::
> +
> +    "255 500 0 500"
> +
> +        ^
> +        |
> +    255 +----+    +----+
> +	|    |    |    |      ...
> +      0 |    +----+    +----
> +        +---------------------->
> +	0    5   10   15     time (100ms)

you're mixing tabs and spaces here, I suggest to use spaces only. Not
sure you want to respin for that.

(I didn't look into the rest of the driver, but assume it's fine.)

Best regards
Uwe


-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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