linux-kernel - Re: [PATCH 0/2] Add QCOM PMIC PWM driver

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Message-Id: <1619635777-2872-1-git-send-email-subbaram@codeaurora.org>
Date:   Wed, 28 Apr 2021 11:49:37 -0700
From:   Subbaraman Narayanamurthy <subbaram@...eaurora.org>
To:     bjorn.andersson@...aro.org
Cc:     aghayal@...eaurora.org, collinsd@...eaurora.org,
        fenglinw@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, subbaram@...eaurora.org
Subject: Re: [PATCH 0/2] Add QCOM PMIC PWM driver

>> Add PWM driver to support PWM modules inside QCOM PMIC chips which are accessed
>> through SPMI bus. Normally, there would be multiple PWM modules with adjacent
>> address spaces present in one PMIC chip, and each PWM module has 0x100 size of
>> address space. With this driver, a pwm_chip with multiple pwm_device individuals
>> is created, and each pwm_device individual is corresponding to one PWM module.
>> 

> Exposing this as individual pwm_chips will prevent us from enabling the
> LED related use cases (patterns and multicolor) that most versions of
> the hardware support.

> I proposed [1] a while ago and think this is a better approach. I'll
> take some time to respin this and send out the next version.

> [1] https://lore.kernel.org/linux-arm-msm/20201021201224.3430546-1-bjorn.andersson@linaro.org/

Hi Bjorn,
Yes, we came across this patch series but this driver (leds-qcom-lpg) is a
combo one which provides support only for RGB LEDs (or TRI_LED module) along
with PWM/LPG channels allocated for it. Say, if we've additional PWM channels
on the same PMIC (that provides user-interface support) or another PMIC
(non user-interface) that has multiple PWM channels that are not used for LED
notifications, it would be good to have a separate PWM driver to support such
channels IMHO. There are couple of use cases we've come across recently.

1. Using a PWM channel for controlling external LCD backlight controller
2. Using a PWM channel for controlling a haptics actuator

Thanks,
Subbaraman

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