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Date:   Mon, 02 Oct 2023 08:09:59 +0200
From:   André Apitzsch <git@...tzsch.eu>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     conor+dt@...nel.org, devicetree@...r.kernel.org,
        krzysztof.kozlowski+dt@...aro.org, lee@...nel.org,
        linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
        pavel@....cz, phone-devel@...r.kernel.org, robh+dt@...nel.org,
        u.kleine-koenig@...gutronix.de,
        ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH v5 2/2] leds: add ktd202x driver

Am Sonntag, dem 01.10.2023 um 22:46 +0200 schrieb Christophe JAILLET:
> Le 01/10/2023 à 18:56, André Apitzsch a écrit :
> > Hi Christophe,
> > 
> > Am Sonntag, dem 01.10.2023 um 17:15 +0200 schrieb Christophe
> > JAILLET:
> > > Le 01/10/2023 à 15:52, André Apitzsch a écrit :
> > > > This commit adds support for Kinetic KTD2026/7 RGB/White LED
> > > > driver.
> > > > 
> > > > Signed-off-by: André Apitzsch
> > > > <git-AtRKszJ1oGPsq35pWSNszA@...lic.gmane.org>
> > > 
> > > ...
> > > 
> > > > +static int ktd202x_setup_led_rgb(struct ktd202x *chip, struct
> > > > device_node *np,
> > > > +                                struct ktd202x_led *led,
> > > > struct
> > > > led_init_data *init_data)
> > > > +{
> > > > +       struct led_classdev *cdev;
> > > > +       struct device_node *child;
> > > > +       struct mc_subled *info;
> > > > +       int num_channels;
> > > > +       int i = 0;
> > > > +       u32 reg;
> > > > +       int ret;
> > > > +
> > > > +       num_channels = of_get_available_child_count(np);
> > > > +       if (!num_channels || num_channels > chip->num_leds)
> > > > +               return -EINVAL;
> > > > +
> > > > +       info = devm_kcalloc(chip->dev, num_channels,
> > > > sizeof(*info),
> > > > GFP_KERNEL);
> > > > +       if (!info)
> > > > +               return -ENOMEM;
> > > > +
> > > > +       for_each_available_child_of_node(np, child) {
> > > > +               u32 mono_color = 0;
> > > 
> > > Un-needed init.
> > > And, why is it defined here, while reg is defined out-side the
> > > loop?
> > 
> > I'll move it out-side the loop (without initialization).
> > 
> > > 
> > > > +
> > > > +               ret = of_property_read_u32(child, "reg", &reg);
> > > > +               if (ret != 0 || reg >= chip->num_leds) {
> > > > +                       dev_err(chip->dev, "invalid 'reg' of
> > > > %pOFn\n", np);
> > > 
> > > Mossing of_node_put(np);?
> > 
> > It shouldn't be needed here if handled in the calling function,
> > right?
> 
> How can the caller do this?
> 
> The goal of this of_node_put() is to release a reference taken by the
> for_each_available_child_of_node() loop, in case of early exit.
> 
> The caller can't know if np needs to be released or not. An error
> code 
> is returned either if an error occurs within the for_each loop, or if
> devm_led_classdev_multicolor_register_ext() fails.
> 
> More over, in your case the caller is ktd202x_add_led().
>  From there either ktd202x_setup_led_rgb() or
> ktd202x_setup_led_single() 
> is called.
> 
> ktd202x_setup_led_single() does not take any reference to np.
> But if it fails, of_node_put() would still be called.
> 
> 

Hello Christophe,

It seems I misunderstood when of_node_put() is used. Thanks for the
explanation.

While checking the usage of of_node_put(), I noticed that dev_err()
(and of_node_put()) should take "child" and not "np", here.

André

> > > 
> > > > +                       return -EINVAL;
> > > > +               }
> > > > +
> > > > +               ret = of_property_read_u32(child, "color",
> > > > &mono_color);
> > > > +               if (ret < 0 && ret != -EINVAL) {
> > > > +                       dev_err(chip->dev, "failed to parse
> > > > 'color'
> > > > of %pOF\n", np);
> > > 
> > > Mossing of_node_put(np);?
> > > 
> > > > +                       return ret;
> > > > +               }
> > > > +
> > > > +               info[i].color_index = mono_color;
> > > > +               info[i].channel = reg;
> > > > +               info[i].intensity = KTD202X_MAX_BRIGHTNESS;
> > > > +               i++;
> > > > +       }
> > > > +
> > > > +       led->mcdev.subled_info = info;
> > > > +       led->mcdev.num_colors = num_channels;
> > > > +
> > > > +       cdev = &led->mcdev.led_cdev;
> > > > +       cdev->brightness_set_blocking =
> > > > ktd202x_brightness_mc_set;
> > > > +       cdev->blink_set = ktd202x_blink_mc_set;
> > > > +
> > > > +       return devm_led_classdev_multicolor_register_ext(chip-
> > > > >dev,
> > > > &led->mcdev, init_data);
> > > > +}
> > > > +
> > > > +static int ktd202x_setup_led_single(struct ktd202x *chip,
> > > > struct
> > > > device_node *np,
> > > > +                                   struct ktd202x_led *led,
> > > > struct
> > > > led_init_data *init_data)
> > > > +{
> > > > +       struct led_classdev *cdev;
> > > > +       u32 reg;
> > > > +       int ret;
> > > > +
> > > > +       ret = of_property_read_u32(np, "reg", &reg);
> > > > +       if (ret != 0 || reg >= chip->num_leds) {
> > > > +               dev_err(chip->dev, "invalid 'reg' of %pOFn\n",
> > > > np);
> > > > +               return -EINVAL;
> > > > +       }
> > > > +       led->index = reg;
> > > > +
> > > > +       cdev = &led->cdev;
> > > > +       cdev->brightness_set_blocking =
> > > > ktd202x_brightness_single_set;
> > > > +       cdev->blink_set = ktd202x_blink_single_set;
> > > > +
> > > > +       return devm_led_classdev_register_ext(chip->dev, &led-
> > > > > cdev, init_data);
> > > > +}
> > > > +
> > > > +static int ktd202x_add_led(struct ktd202x *chip, struct
> > > > device_node *np, unsigned int index)
> > > > +{
> > > > +       struct ktd202x_led *led = &chip->leds[index];
> > > > +       struct led_init_data init_data = {};
> > > > +       struct led_classdev *cdev;
> > > > +       u32 color = 0;
> > > Un-needed init.
> > > 
> > > > +       int ret;
> > > > +
> > > > +       /* Color property is optional in single color case */
> > > > +       ret = of_property_read_u32(np, "color", &color);
> > > > +       if (ret < 0 && ret != -EINVAL) {
> > > > +               dev_err(chip->dev, "failed to parse 'color' of
> > > > %pOF\n", np);
> > > > +               return ret;
> > > > +       }
> > > > +
> > > > +       led->chip = chip;
> > > > +       init_data.fwnode = of_fwnode_handle(np);
> > > > +
> > > > +       if (color == LED_COLOR_ID_RGB) {
> > > > +               cdev = &led->mcdev.led_cdev;
> > > > +               ret = ktd202x_setup_led_rgb(chip, np, led,
> > > > &init_data);
> > > > +       } else {
> > > > +               cdev = &led->cdev;
> > > > +               ret = ktd202x_setup_led_single(chip, np, led,
> > > > &init_data);
> > > > +       }
> > > > +
> > > > +       if (ret) {
> > > > +               dev_err(chip->dev, "unable to register %s\n",
> > > > cdev-
> > > > > name);
> > > > +               of_node_put(np);
> > > 
> > > This is strange to have it here.
> > > Why not above after "if (ret < 0 && ret != -EINVAL) {"?
> > > 
> > > It would look much more natural to have it a few lines below, ...
> > > [1]
> > 
> > Good catch. I'll move of_node_put(np); to [1] and [2].
> 
> Why [2]?
> It does not seem needed here.
> 
> of_get_available_child_count() does not keep any reference.
> 
> CJ
> 
> > 
> > > 
> > > > +               return ret;
> > > > +       }
> > > > +
> > > > +       cdev->max_brightness = KTD202X_MAX_BRIGHTNESS;
> > > > +
> > > > +       return 0;
> > > > +}
> > > > +
> > > > +static int ktd202x_probe_dt(struct ktd202x *chip)
> > > > +{
> > > > +       struct device_node *np = dev_of_node(chip->dev),
> > > > *child;
> > > > +       unsigned int i;
> > > > +       int count, ret;
> > > > +
> > > > +       chip->num_leds = (int)(unsigned
> > > > long)of_device_get_match_data(chip->dev);
> > > > +
> > > > +       count = of_get_available_child_count(np);
> > > > +       if (!count || count > chip->num_leds)
> > 
> > [2].
> > 
> > > > +               return -EINVAL;
> > > > +
> > > > +       regmap_write(chip->regmap, KTD202X_REG_RESET_CONTROL,
> > > > KTD202X_RSTR_RESET);
> > > > +
> > > > +       /* Allow the device to execute the complete reset */
> > > > +       usleep_range(200, 300);
> > > > +
> > > > +       i = 0;
> > > > +       for_each_available_child_of_node(np, child) {
> > > > +               ret = ktd202x_add_led(chip, child, i);
> > > > +               if (ret)
> > > 
> > > [1] ... here.
> > > 
> > > Otherwise, it is likely that, thanks to a static checker, an
> > > additionnal
> > > of_node_put() will be added on early exit of the loop.
> > > 
> > > CJ
> > > 
> > > > +                       return ret;
> > > > +               i++;
> > > > +       }
> > > > +
> > > > +       return 0;
> > > > +}
> > > 
> > > ...
> > > 
> > 
> > Best regards,
> > André
> > 
> 

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