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

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Date:   Wed, 14 Nov 2018 11:36:52 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Chanwoo Choi <cw00.choi@...sung.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 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.

API inside the kernel are not carved in the stone.


-- 
With Best Regards,
Andy Shevchenko