linux-kernel - Re: [PATCH v1 2/5] extcon: Return -EPROBE_DEFER when extcon device is not found

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Message-id: <5BEBEF7C.7060003@samsung.com>
Date:   Wed, 14 Nov 2018 18:48:44 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        USB <linux-usb@...r.kernel.org>, Felipe Balbi <balbi@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        "Krogerus, Heikki" <heikki.krogerus@...ux.intel.com>,
        rogerq@...com, Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sebastian Reichel <sre@...nel.org>,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
        Darren Hart <dvhart@...radead.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Hans de Goede <hdegoede@...hat.com>
Subject: Re: [PATCH v1 2/5] extcon: Return -EPROBE_DEFER when extcon device
 is not found

On 2018년 11월 14일 18:36, Andy Shevchenko wrote:
> On Wed, Nov 14, 2018 at 06:13:37PM +0900, Chanwoo Choi wrote:
>> On 2018년 11월 14일 17:35, Andy Shevchenko wrote:
>>> On Wed, Nov 14, 2018 at 1:53 AM Chanwoo Choi <cw00.choi@...sung.com> wrote:
>>>
>>>> I was thinking about again to change from NULL to EPROBE_DEFER.
>>>>
>>>> extcon_get_extcon_dev() function was almost called in the probe function.
>>>> But, this function might be called on other position instead of probe.
>>>
>>> *Might be* sounds like a theoretical thing, care to share what is in you mind?
>>> Current users and more important the new coming one are *all* doing the same.
>>>
>>>> ENODEV is more correct error instead of EPROBE_DEFER.
>>>
>>> So, you are proposing to continue duplicating conversion from ENODEV
>>> to EPROBE_DEFER in *each* caller?
>>
>> The extcon core don't know the caller situation is in either probe() or other position
>> in the caller driver. The caller driver should decide the kind of error value
>> by using the return value of extcon_get_extcon_dev().
>>
>> extcon_get_extcon_dev() function cannot be modified for only one case.
>> If some device driver call extcon_get_extcon_dev() out of probe() fuction,
>> EPROBE_DEFER is not always correct.
> 
> I agree with this, but look at the current state of affairs. All users do the same.
> If we need to have another case we may consider this later.

Because we know the potential wrong case of this change, I can't agree this change.
If extcon_get_extcon_dev() returns ENODEV instead of EPROBE_DEFER,
it is clear and then there are no problem on both current and future.

> 
> API inside the kernel are not carved in the stone.
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics