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

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Message-ID: <CAD=FV=Xj5k7JROP1PFY9tmXxLY7FRJNdr-+UmkCW_YGqpDkFew@mail.gmail.com>
Date:   Fri, 18 Feb 2022 08:10:50 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Pavel Machek <pavel@....cz>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        Satya Priya Kakitapalli <c_skakit@....qualcomm.com>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        Luca Weiss <luca@...tu.xyz>, Rob Herring <robh+dt@...nel.org>,
        linux-leds@...r.kernel.org,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-pwm <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v12 2/2] leds: Add driver for Qualcomm LPG

Hi,

On Tue, Feb 15, 2022 at 8:54 PM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> +static int lpg_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +                        const struct pwm_state *state)
> +{
> +       struct lpg *lpg = container_of(chip, struct lpg, pwm);
> +       struct lpg_channel *chan = &lpg->channels[pwm->hwpwm];
> +       int ret;
> +
> +       if (state->polarity != PWM_POLARITY_NORMAL)
> +               return -EINVAL;
> +
> +       mutex_lock(&lpg->lock);
> +
> +       if (state->enabled) {
> +               ret = lpg_calc_freq(chan, state->period);
> +               if (ret < 0)
> +                       goto out_unlock;
> +
> +               lpg_calc_duty(chan, state->duty_cycle);
> +       }
> +       chan->enabled = state->enabled;
> +
> +       lpg_apply(chan);
> +
> +       triled_set(lpg, chan->triled_mask, chan->enabled ? chan->triled_mask : 0);
> +
> +out_unlock:
> +       mutex_unlock(&lpg->lock);
> +
> +       return ret;
> +}

My compiler (correctly) yelled that `ret` is returned uninitialized if
`state->enabled` is false. I initialized `ret` to 0 and the problem
went away. I assume that the patch will need to spin to fix that
unless everything else looks great and a maintainer wants to fix that
when applying.

With that fix, I was able to use Bjorn's patch along with Satya's
patches adding pm8350c support (removing the now defunct
"pwm_9bit_mask" property) to make the PWM on my board work. Thus, once
the error my compiler complained about is fixed I'm happy with my
`Tested-by` being added.

For now I haven't actually reviewed the code here, but if folks feel
like it needs an extra pair of eyes then please yell and I'll find
some time to do it.

-Doug