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

Hi Daniel,

Thanks for your comments!

Daniel Thompson [off-list ref] 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:

quoted

From: ChiaEn Wu <redacted>

Add Mediatek MT6370 Backlight support.

Signed-off-by: ChiaEn Wu <redacted>

quoted

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!

quoted

+              */
+             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.

quoted

<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.

quoted

Best regards,
ChiaEn Wu