linux-kernel - Re: [PATCH v3] extcon: palmas: hide error messages if gpio returns -EPROBE

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Date:   Mon, 17 Feb 2020 19:38:16 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Ladislav Michl <ladis@...ux-mips.org>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        linux-kernel@...r.kernel.org, letux-kernel@...nphoenux.org,
        kernel@...a-handheld.com, linux-omap@...r.kernel.org
Subject: Re: [PATCH v3] extcon: palmas: hide error messages if gpio returns -EPROBE_DEFER

Hi,

> Am 17.02.2020 um 19:29 schrieb Ladislav Michl <ladis@...ux-mips.org>:
> 
> On Mon, Feb 17, 2020 at 02:58:14PM +0100, H. Nikolaus Schaller wrote:
>> 
>>> Am 17.02.2020 um 14:38 schrieb H. Nikolaus Schaller <hns@...delico.com>:
>>> 
>>> 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 | 8 ++++++--
>>> 1 file changed, 6 insertions(+), 2 deletions(-)
>>> 
>>> diff --git a/drivers/extcon/extcon-palmas.c b/drivers/extcon/extcon-palmas.c
>>> index edc5016f46f1..cea58d0cb457 100644
>>> --- a/drivers/extcon/extcon-palmas.c
>>> +++ b/drivers/extcon/extcon-palmas.c
>>> @@ -205,14 +205,18 @@ 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)) {
>>> +	if (PTR_ERR(palmas_usb->id_gpiod) == -EPROBE_DEFER) {
>>> +		return -EPROBE_DEFER;
>>> +	} else if (IS_ERR(palmas_usb->id_gpiod)) {
>> 
>> Hm.
>> 
>> While looking again at that: why do we need the "{" and "} else "?
>> 
>> It should be sufficient to have
>> 
>>> 	palmas_usb->id_gpiod = devm_gpiod_get_optional(&pdev->dev, "id",
>>> 							GPIOD_IN);
>>> +	if (PTR_ERR(palmas_usb->id_gpiod) == -EPROBE_DEFER)
>>> +		return -EPROBE_DEFER;
>>> 	if (IS_ERR(palmas_usb->id_gpiod)) {
>> 
>> What do you think is better coding style here?
> 
> How about something like this? (just an idea with some work left for you ;-))
> 
> --- a/drivers/extcon/extcon-palmas.c
> +++ b/drivers/extcon/extcon-palmas.c
> @@ -206,8 +206,10 @@ 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");
> -		return PTR_ERR(palmas_usb->id_gpiod);
> +		status = PTR_ERR(palmas_usb->id_gpiod);
> +		if (status != -EPROBE_DEFER)
> +			dev_err(&pdev->dev, "failed to get id gpio: %d\n", status);
> +		return status;
> 	}

Well, what would be the improvement?
It needs an additional variable and makes the change more complex.

The main suggestion by Chanwoo Choi was to move the check for EPROBE_DEFER
outside of the IS_ERR() because checking this first and then for EPROBE_DEFER
is not necessary.

If acceptable I'd prefer my last proposal. It just adds 2 LOC before
and without touching the existing if (IS_ERR(...)).

If the compiler is clever it can cache palmas_usb->id_gpiod in a register
which serves the same purpose as the status variable.

> 
> 	palmas_usb->vbus_gpiod = devm_gpiod_get_optional(&pdev->dev, "vbus",

BR and thanks,
Nikolaus