Subject: Re: [PATCH v3] extcon: fix extcon_get_extcon_dev() error handling
To:     Dan Carpenter <dan.carpenter@oracle.com>,
        MyungJoo Ham <myungjoo.ham@samsung.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Sebastian Reichel <sre@kernel.org>,
        Felipe Balbi <balbi@kernel.org>
Cc:     Chen-Yu Tsai <wens@csie.org>, Hans de Goede <hdegoede@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        linux-usb@vger.kernel.org, linux-omap@vger.kernel.org,
        kernel-janitors@vger.kernel.org
From:   Chanwoo Choi <cw00.choi@samsung.com>
Organization: Samsung Electronics
Message-ID: <e0adc445-ede3-171a-0c1b-8667792d4c3e@samsung.com>
Date:   Mon, 20 Dec 2021 10:20:53 +0900
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:59.0) Gecko/20100101
        Thunderbird/59.0
MIME-Version: 1.0
In-Reply-To: <20211217062846.GA26548@kili>
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset="utf-8"
CMS-TYPE: 101P
DLP-Filter: Pass
References: <CGME20211217062932epcas1p1b262f3dd17607f5e42b85c169729ce63@epcas1p1.samsung.com>
        <20211217062846.GA26548@kili>
Precedence: bulk

Hi Sebastian and Felipe,

If Sebastian and Felipe don't have any additional opinion,
could you please reply the review for this patch?

And if Sebastian and Felipe agree, I'll merge it to extcon tree.


Best Regards,
Chanwoo Choi


On 12/17/21 3:28 PM, Dan Carpenter wrote:
> The extcon_get_extcon_dev() function returns error pointers on error,
> NULL when it's a -EPROBE_DEFER defer situation, and ERR_PTR(-ENODEV)
> when the CONFIG_EXTCON option is disabled.  This is very complicated for
> the callers to handle and a number of them had bugs that would lead to
> an Oops.
> 
> In real life, there are two things which prevented crashes.  First,
> error pointers would only be returned if there was bug in the caller
> where they passed a NULL "extcon_name" and none of them do that.
> Second, only two out of the eight drivers will build when CONFIG_EXTCON
> is disabled.
> 
> The normal way to write this would be to return -EPROBE_DEFER directly
> when appropriate and return NULL when CONFIG_EXTCON is disabled.  Then
> the error handling is simple and just looks like:
> 
> 	dev->edev = extcon_get_extcon_dev(acpi_dev_name(adev));
> 	if (IS_ERR(dev->edev))
> 		return PTR_ERR(dev->edev);
> 
> For the two drivers which can build with CONFIG_EXTCON disabled, then
> extcon_get_extcon_dev() will now return NULL which is not treated as an
> error and the probe will continue successfully.  Those two drivers are
> "typec_fusb302" and "max8997-battery".  In the original code, the
> typec_fusb302 driver had an 800ms hang in tcpm_get_current_limit() but
> now that function is a no-op.  For the max8997-battery driver everything
> should continue working as is.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> v2: return NULL when CONFIG_EXTCON is disabled
> v3: Add a note to extcon_get_extcon_dev() to say that it may only be
>     called from probe().
> 
>  drivers/extcon/extcon.c                |  4 +++-
>  include/linux/extcon.h                 |  2 +-
>  drivers/extcon/extcon-axp288.c         |  4 ++--
>  drivers/power/supply/axp288_charger.c  | 17 ++++++++++-------
>  drivers/power/supply/charger-manager.c |  7 ++-----
>  drivers/power/supply/max8997_charger.c | 10 +++++-----
>  drivers/usb/dwc3/drd.c                 |  9 ++-------
>  drivers/usb/phy/phy-omap-otg.c         |  4 ++--
>  drivers/usb/typec/tcpm/fusb302.c       |  4 ++--
>  9 files changed, 29 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/extcon/extcon.c b/drivers/extcon/extcon.c
> index e7a9561a826d..9eb92997f3ae 100644
> --- a/drivers/extcon/extcon.c
> +++ b/drivers/extcon/extcon.c
> @@ -863,6 +863,8 @@ EXPORT_SYMBOL_GPL(extcon_set_property_capability);
>   * @extcon_name:	the extcon name provided with extcon_dev_register()
>   *
>   * Return the pointer of extcon device if success or ERR_PTR(err) if fail.
> + * NOTE: This function returns -EPROBE_DEFER so it may only be called from
> + * probe() functions.
>   */
>  struct extcon_dev *extcon_get_extcon_dev(const char *extcon_name)
>  {
> @@ -876,7 +878,7 @@ struct extcon_dev *extcon_get_extcon_dev(const char *extcon_name)
>  		if (!strcmp(sd->name, extcon_name))
>  			goto out;
>  	}
> -	sd = NULL;
> +	sd = ERR_PTR(-EPROBE_DEFER);
>  out:
>  	mutex_unlock(&extcon_dev_list_lock);
>  	return sd;
> diff --git a/include/linux/extcon.h b/include/linux/extcon.h
> index 0c19010da77f..685401d94d39 100644
> --- a/include/linux/extcon.h
> +++ b/include/linux/extcon.h
> @@ -296,7 +296,7 @@ static inline void devm_extcon_unregister_notifier_all(struct device *dev,
>  
>  static inline struct extcon_dev *extcon_get_extcon_dev(const char *extcon_name)
>  {
> -	return ERR_PTR(-ENODEV);
> +	return NULL;
>  }
>  
>  static inline struct extcon_dev *extcon_find_edev_by_node(struct device_node *node)
> diff --git a/drivers/extcon/extcon-axp288.c b/drivers/extcon/extcon-axp288.c
> index 7c6d5857ff25..180be768c215 100644
> --- a/drivers/extcon/extcon-axp288.c
> +++ b/drivers/extcon/extcon-axp288.c
> @@ -394,8 +394,8 @@ static int axp288_extcon_probe(struct platform_device *pdev)
>  		if (adev) {
>  			info->id_extcon = extcon_get_extcon_dev(acpi_dev_name(adev));
>  			put_device(&adev->dev);
> -			if (!info->id_extcon)
> -				return -EPROBE_DEFER;
> +			if (IS_ERR(info->id_extcon))
> +				return PTR_ERR(info->id_extcon);
>  
>  			dev_info(dev, "controlling USB role\n");
>  		} else {
> diff --git a/drivers/power/supply/axp288_charger.c b/drivers/power/supply/axp288_charger.c
> index ec41f6cd3f93..4acfeb52a44e 100644
> --- a/drivers/power/supply/axp288_charger.c
> +++ b/drivers/power/supply/axp288_charger.c
> @@ -848,17 +848,20 @@ static int axp288_charger_probe(struct platform_device *pdev)
>  	info->regmap_irqc = axp20x->regmap_irqc;
>  
>  	info->cable.edev = extcon_get_extcon_dev(AXP288_EXTCON_DEV_NAME);
> -	if (info->cable.edev == NULL) {
> -		dev_dbg(dev, "%s is not ready, probe deferred\n",
> -			AXP288_EXTCON_DEV_NAME);
> -		return -EPROBE_DEFER;
> +	if (IS_ERR(info->cable.edev)) {
> +		dev_err_probe(dev, PTR_ERR(info->cable.edev),
> +			      "extcon_get_extcon_dev(%s) failed\n",
> +			      AXP288_EXTCON_DEV_NAME);
> +		return PTR_ERR(info->cable.edev);
>  	}
>  
>  	if (acpi_dev_present(USB_HOST_EXTCON_HID, NULL, -1)) {
>  		info->otg.cable = extcon_get_extcon_dev(USB_HOST_EXTCON_NAME);
> -		if (info->otg.cable == NULL) {
> -			dev_dbg(dev, "EXTCON_USB_HOST is not ready, probe deferred\n");
> -			return -EPROBE_DEFER;
> +		if (IS_ERR(info->otg.cable)) {
> +			dev_err_probe(dev, PTR_ERR(info->otg.cable),
> +				      "extcon_get_extcon_dev(%s) failed\n",
> +				      USB_HOST_EXTCON_NAME);
> +			return PTR_ERR(info->otg.cable);
>  		}
>  		dev_info(dev, "Using " USB_HOST_EXTCON_HID " extcon for usb-id\n");
>  	}
> diff --git a/drivers/power/supply/charger-manager.c b/drivers/power/supply/charger-manager.c
> index d67edb760c94..92db79400a6a 100644
> --- a/drivers/power/supply/charger-manager.c
> +++ b/drivers/power/supply/charger-manager.c
> @@ -985,13 +985,10 @@ static int charger_extcon_init(struct charger_manager *cm,
>  	cable->nb.notifier_call = charger_extcon_notifier;
>  
>  	cable->extcon_dev = extcon_get_extcon_dev(cable->extcon_name);
> -	if (IS_ERR_OR_NULL(cable->extcon_dev)) {
> +	if (IS_ERR(cable->extcon_dev)) {
>  		pr_err("Cannot find extcon_dev for %s (cable: %s)\n",
>  			cable->extcon_name, cable->name);
> -		if (cable->extcon_dev == NULL)
> -			return -EPROBE_DEFER;
> -		else
> -			return PTR_ERR(cable->extcon_dev);
> +		return PTR_ERR(cable->extcon_dev);
>  	}
>  
>  	for (i = 0; i < ARRAY_SIZE(extcon_mapping); i++) {
> diff --git a/drivers/power/supply/max8997_charger.c b/drivers/power/supply/max8997_charger.c
> index 25207fe2aa68..634658adf313 100644
> --- a/drivers/power/supply/max8997_charger.c
> +++ b/drivers/power/supply/max8997_charger.c
> @@ -248,13 +248,13 @@ static int max8997_battery_probe(struct platform_device *pdev)
>  		dev_info(&pdev->dev, "couldn't get charger regulator\n");
>  	}
>  	charger->edev = extcon_get_extcon_dev("max8997-muic");
> -	if (IS_ERR_OR_NULL(charger->edev)) {
> -		if (!charger->edev)
> -			return -EPROBE_DEFER;
> -		dev_info(charger->dev, "couldn't get extcon device\n");
> +	if (IS_ERR(charger->edev)) {
> +		dev_err_probe(charger->dev, PTR_ERR(charger->edev),
> +			      "couldn't get extcon device: max8997-muic\n");
> +		return PTR_ERR(charger->edev);
>  	}
>  
> -	if (!IS_ERR(charger->reg) && !IS_ERR_OR_NULL(charger->edev)) {
> +	if (!IS_ERR(charger->reg)) {
>  		INIT_WORK(&charger->extcon_work, max8997_battery_extcon_evt_worker);
>  		ret = devm_add_action(&pdev->dev, max8997_battery_extcon_evt_stop_work, charger);
>  		if (ret) {
> diff --git a/drivers/usb/dwc3/drd.c b/drivers/usb/dwc3/drd.c
> index d7f76835137f..a490f79131c1 100644
> --- a/drivers/usb/dwc3/drd.c
> +++ b/drivers/usb/dwc3/drd.c
> @@ -454,13 +454,8 @@ static struct extcon_dev *dwc3_get_extcon(struct dwc3 *dwc)
>  	 * This device property is for kernel internal use only and
>  	 * is expected to be set by the glue code.
>  	 */
> -	if (device_property_read_string(dev, "linux,extcon-name", &name) == 0) {
> -		edev = extcon_get_extcon_dev(name);
> -		if (!edev)
> -			return ERR_PTR(-EPROBE_DEFER);
> -
> -		return edev;
> -	}
> +	if (device_property_read_string(dev, "linux,extcon-name", &name) == 0)
> +		return extcon_get_extcon_dev(name);
>  
>  	/*
>  	 * Try to get an extcon device from the USB PHY controller's "port"
> diff --git a/drivers/usb/phy/phy-omap-otg.c b/drivers/usb/phy/phy-omap-otg.c
> index ee0863c6553e..6e6ef8c0bc7e 100644
> --- a/drivers/usb/phy/phy-omap-otg.c
> +++ b/drivers/usb/phy/phy-omap-otg.c
> @@ -95,8 +95,8 @@ static int omap_otg_probe(struct platform_device *pdev)
>  		return -ENODEV;
>  
>  	extcon = extcon_get_extcon_dev(config->extcon);
> -	if (!extcon)
> -		return -EPROBE_DEFER;
> +	if (IS_ERR(extcon))
> +		return PTR_ERR(extcon);
>  
>  	otg_dev = devm_kzalloc(&pdev->dev, sizeof(*otg_dev), GFP_KERNEL);
>  	if (!otg_dev)
> diff --git a/drivers/usb/typec/tcpm/fusb302.c b/drivers/usb/typec/tcpm/fusb302.c
> index 72f9001b0792..96c55eaf3f80 100644
> --- a/drivers/usb/typec/tcpm/fusb302.c
> +++ b/drivers/usb/typec/tcpm/fusb302.c
> @@ -1708,8 +1708,8 @@ static int fusb302_probe(struct i2c_client *client,
>  	 */
>  	if (device_property_read_string(dev, "linux,extcon-name", &name) == 0) {
>  		chip->extcon = extcon_get_extcon_dev(name);
> -		if (!chip->extcon)
> -			return -EPROBE_DEFER;
> +		if (IS_ERR(chip->extcon))
> +			return PTR_ERR(chip->extcon);
>  	}
>  
>  	chip->vbus = devm_regulator_get(chip->dev, "vbus");
>