linux-kernel - Re: [PATCH v3 14/14] video: backlight: mt6370: Add Mediatek MT6370 support

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Date:   Fri, 24 Jun 2022 17:56:41 +0800
From:   ChiaEn Wu <peterwu.pub@...il.com>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Lee Jones <lee.jones@...aro.org>, jingoohan1@...il.com,
        pavel@....cz, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, matthias.bgg@...il.com,
        sre@...nel.org, chunfeng.yun@...iatek.com,
        gregkh@...uxfoundation.org, Jonathan Cameron <jic23@...nel.org>,
        lars@...afoo.de, lgirdwood@...il.com, broonie@...nel.org,
        linux@...ck-us.net, heikki.krogerus@...ux.intel.com, deller@....de,
        ChiaEn Wu <chiaen_wu@...htek.com>,
        Alice Chen <alice_chen@...htek.com>,
        ChiYuan Huang <cy_huang@...htek.com>,
        dri-devel@...ts.freedesktop.org, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-iio@...r.kernel.org, linux-fbdev@...r.kernel.org,
        szunichen@...il.com
Subject: Re: [PATCH v3 14/14] video: backlight: mt6370: Add Mediatek MT6370 support

Hi Daniel,

Thanks for your comments!

Daniel Thompson <daniel.thompson@...aro.org> 於 2022年6月23日 週四 晚上9:43寫道：
>
> On Thu, Jun 23, 2022 at 07:56:31PM +0800, ChiaEn Wu wrote:
> > From: ChiaEn Wu <chiaen_wu@...htek.com>
> >
> > Add Mediatek MT6370 Backlight support.
> >
> > Signed-off-by: ChiaEn Wu <chiaen_wu@...htek.com>
>
> > diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
> > index a003e02..7cd823d 100644
> > <snip>
> > +static int mt6370_init_backlight_properties(struct mt6370_priv *priv,
> > +                                         struct backlight_properties *props)
> > +{
> > +     struct device *dev = priv->dev;
> > +     u8 prop_val;
> > +     u32 brightness, ovp_uV, ocp_uA;
> > +     unsigned int mask, val;
> > +     int ret;
> > +
> > +     /* Vendor optional properties */
> > +     val = 0;
> > +     if (device_property_read_bool(dev, "mediatek,bled-pwm-enable"))
> > +             val |= MT6370_BL_PWM_EN_MASK;
> > +
> > +     if (device_property_read_bool(dev, "mediatek,bled-pwm-hys-enable"))
> > +             val |= MT6370_BL_PWM_HYS_EN_MASK;
> > +
> > +     ret = device_property_read_u8(dev,
> > +                                   "mediatek,bled-pwm-hys-input-th-steps",
> > +                                   &prop_val);
> > +     if (!ret) {
> > +             prop_val = clamp_val(prop_val,
> > +                                  MT6370_BL_PWM_HYS_TH_MIN_STEP,
> > +                                  MT6370_BL_PWM_HYS_TH_MAX_STEP);
> > +             /*
> > +              * prop_val =  1      -->  1 steps --> 0x00
> > +              * prop_val =  2 ~  4 -->  4 steps --> 0x01
> > +              * prop_val =  5 ~ 16 --> 16 steps --> 0x10
> > +              * prop_val = 17 ~ 64 --> 64 steps --> 0x11
>
>                                                       ^^^^^
> These numbers are binary, not hex, right? If so, the comments
> should be 0b00 to 0b03 .

Ohh! Yes! These numbers are binary!
I so apologize for making this mistake...
I will revise the comments in the next patch!
Thank you so much!

>
>
> > +              */
> > +             prop_val = (ilog2(roundup_pow_of_two(prop_val)) + 1) >> 1;
> > +             val |= prop_val << (ffs(MT6370_BL_PWM_HYS_SEL_MASK) - 1);
> > +     }
> > +
> > +     ret = regmap_update_bits(priv->regmap, MT6370_REG_BL_PWM,
> > +                              val, val);
> > +     if (ret)
> > +             return ret;
>
> Overall, I like this approach! Easy to read and understand.
>
>
> > <snip>
> > +static int mt6370_bl_probe(struct platform_device *pdev)
> > +{
> > +     struct mt6370_priv *priv;
> > +     struct backlight_properties props = {
> > +             .type = BACKLIGHT_RAW,
> > +             .scale = BACKLIGHT_SCALE_LINEAR,
>
> Sorry, I missed this before but the KConfig comment says that the
> backlight can support both linear and exponential curves.
>
> Is there a good reason to default to linear?

Well...
The customers who used this PMIC have very few or even no use exponential curve,
so I set the default to linear.

If you think this is inappropriate, I will add a DT property to
control this feature in the next patch!

By the way,
I found some mistakes in my probe() function... I didn't use "return"
when I use dev_err_probe()...
I will refine it in the next patch!

>
>
> Daniel.
> >

Best regards,
ChiaEn Wu