linux-kernel - Re: [PATCH] extcon: palmas: hide error messages if gpio returns -EPROBE

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Date:   Mon, 17 Feb 2020 13:21:30 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Chanwoo Choi <cw00.choi@...sung.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        linux-kernel@...r.kernel.org, letux-kernel@...nphoenux.org,
        kernel@...a-handheld.com, linux-omap@...r.kernel.org
Subject: Re: [PATCH] extcon: palmas: hide error messages if gpio returns -EPROBE_DEFER

Hi,

> Am 17.02.2020 um 12:24 schrieb Chanwoo Choi <cw00.choi@...sung.com>:
> 
> Hi,
> 
> On 2/17/20 8:07 PM, H. Nikolaus Schaller wrote:
>> Hi Chanwoo Choi,
>> 
>>> Am 17.02.2020 um 11:15 schrieb Chanwoo Choi <cw00.choi@...sung.com>:
>>> 
>>> Hi,
>>> 
>>> On 2/17/20 5:55 PM, H. Nikolaus Schaller wrote:
>>>> If the gpios are probed after this driver (e.g. if they
>>>> come from an i2c expander) there is no need to print an
>>>> error message.
>>>> 
>>>> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
>>>> ---
>>>> drivers/extcon/extcon-palmas.c | 6 ++++--
>>>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>>> 
>>>> diff --git a/drivers/extcon/extcon-palmas.c b/drivers/extcon/extcon-palmas.c
>>>> index edc5016f46f1..9c6254c0531c 100644
>>>> --- a/drivers/extcon/extcon-palmas.c
>>>> +++ b/drivers/extcon/extcon-palmas.c
>>>> @@ -206,14 +206,16 @@ static int palmas_usb_probe(struct platform_device *pdev)
>>>> 	palmas_usb->id_gpiod = devm_gpiod_get_optional(&pdev->dev, "id",
>>>> 							GPIOD_IN);
>>>> 	if (IS_ERR(palmas_usb->id_gpiod)) {
>>>> -		dev_err(&pdev->dev, "failed to get id gpio\n");
>>>> +		if (PTR_ERR(palmas_usb->id_gpiod) != -EPROBE_DEFER)
>>>> +			dev_err(&pdev->dev, "failed to get id gpio\n");
>>>> 		return PTR_ERR(palmas_usb->id_gpiod);
>>>> 	}
> 
> 
> How about editing it ? as following:
> because following suggestion reduces the one checking behavior
> when return value is -EPROBE_DEFER.
> 
> 	if (PTR_ERR(palmas_usb->id_gpiod) == -EPROBE_DEFER) {
> 		return -EPROBE_DEFER;
> 	} else if (IS_ERR(palmas_usb->id_gpiod)) {
> 		dev_err(&pdev->dev, "failed to get id gpio\n");
> 		return PTR_ERR(palmas_usb->id_gpiod);
> 	}

Yes, looks indeed to be valid (some discussion around
is here: https://lore.kernel.org/patchwork/patch/999602/ ).

So I'll send an update asap.

> 
>>>> 
>>>> 	palmas_usb->vbus_gpiod = devm_gpiod_get_optional(&pdev->dev, "vbus",
>>>> 							GPIOD_IN);
>>>> 	if (IS_ERR(palmas_usb->vbus_gpiod)) {
>>>> -		dev_err(&pdev->dev, "failed to get vbus gpio\n");
>>>> +		if (PTR_ERR(palmas_usb->vbus_gpiod) != -EPROBE_DEFER)
>>>> +			dev_err(&pdev->dev, "failed to get vbus gpio\n");
> 
> ditto.
> 
>>>> 		return PTR_ERR(palmas_usb->vbus_gpiod);
>>>> 	}
>>>> 
>>>> 
>>> 
>>> Usually, gpio driver like pinctrl is very early probed
>>> because almost device drivers should use gpio.
>>> So, I have not any experience about this situation.
>>> Do you meet this situation on any h/w board?
>> 
>> Yes, I have experienced that sometimes on omap5+palmas based boards.
>> 
>> It seems to be this:
>> 
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap5-board-common.dtsi?h=v5.6-rc2#n384
>> 
>> The extcon_usb3 can potentially match this extcon-palmas driver at
>> a moment where the palmas_gpio it is referring to has not yet been
>> successfully probed. Then the palmas_gpio would return -EPROBE_DEFER.
>> 
>> AFAIK there is no guarantee for a specific sequence of drivers
>> being probed and it is pure luck that in most cases the gpios
>> are already probed.
> 
> Thanks for explaining the example.

BR and thanks,
Nikolaus Schaller