linux-kernel - Re: [PATCH v2] extcon: fix extcon_get_extcon

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Date:   Thu, 16 Dec 2021 10:08:36 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Chanwoo Choi <cw00.choi@...sung.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Sebastian Reichel <sre@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>, Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-omap@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2] extcon: fix extcon_get_extcon_dev() error handling

Hi,

On 12/16/21 09:05, Dan Carpenter wrote:
> On Thu, Dec 16, 2021 at 05:24:30PM +0900, Chanwoo Choi wrote:
>> On 12/16/21 4:52 PM, Dan Carpenter wrote:
>>> On Thu, Dec 16, 2021 at 03:39:46PM +0900, Chanwoo Choi wrote:
>>>> Hi Dan,
>>>>
>>>> First of all,  sorry for late reply.
>>>>
>>>> There is one issue. About this issue, I already discussed on patch[1]
>>>> [1] https://lore.kernel.org/lkml/5BEB63C3.1020504@samsung.com/  
>>>>
>>>> extcon_get_extcon_dev() is used for anywhere except for probe step.
>>>> But EPROBE_DEFER is only used on probe step.
>>>>
>>>> So that it is not clear to return EPROBE_DEFER from extcon_get_extcon_dev()
>>>> because extcon_get_extcon_dev() never know either call it on probe function
>>>> or not.
>>>
>>> Currently extcon_get_extcon_dev() is only called from probe so it's not
>>> an issue.
>>
>> Even if extcon_get_extcon_dev() is used on probe until now,
>> it is possible to use on anywhere as I commented.
>>
>> It is difficult to agree this approach without any other solution.
>>
>> Basically, the subsystem core never know either probe time or not.
>> It means that this issue should be handled in each device driver.
>>
> 
> To be honest, I'm not sure how this differs from other functions which
> return -EPROBE_DEFER.  How do other functions guarantee they will only
> be called from probe()?

Right I have to agree with Dan here, all "get" functons for resources
like gpios, clks, regulators, phys, pwms, etc. may return -EPROBE_DEFER
and since these functions may return -EPROBE_DEFER they *must* only be
called from a driver's probe() function.

So I believe that the solution here is to simply add a kernel-doc comment
on extcon_get_extcon_dev() which documents that it may return -EPROBE_DEFER
and that it thus *must* only be called from a driver's probe() function.

Regards,

Hans



> 
> regards,
> dan carpenter
>