linux-kernel - Re: [PATCH v2 2/2] IIO: st_accel_i2c.c: Use probe

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Message-ID: <alpine.DEB.2.20.1807041119360.8194@fox.voss.local>
Date:   Wed, 4 Jul 2018 11:42:40 +0200 (CEST)
From:   Nikolaus Voss <nikolaus.voss@...wensteinmedical.de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Lorenzo Bianconi <lorenzo.bianconi83@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Xiongfeng Wang <xiongfeng.wang@...aro.org>,
        linux-iio@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        nv@...n.de
Subject: Re: [PATCH v2 2/2] IIO: st_accel_i2c.c: Use probe_new() instead of
 probe()

On Wed, 4 Jul 2018, Andy Shevchenko wrote:
> On Wed, Jul 4, 2018 at 12:09 PM, Nikolaus Voss
> <nikolaus.voss@...wensteinmedical.de> wrote:
>> On Wed, 4 Jul 2018, Andy Shevchenko wrote:
>>>
>>> On Wed, Jul 4, 2018 at 9:37 AM, Nikolaus Voss
>>> <nikolaus.voss@...wensteinmedical.de> wrote:
>>>>
>>>> On Wed, 4 Jul 2018, Andy Shevchenko wrote:
>>>>>
>>>>>
>>>>> On Tue, Jul 3, 2018 at 9:06 AM, Nikolaus Voss
>>>>> <nikolaus.voss@...wensteinmedical.de> wrote:
>>>>>>
>>>>>>
>>>>>> struct i2c_device_id argument of probe() is not used, so use
>>>>>> probe_new()
>>>>>> instead.
>>>>>>
>>>>>
>>>>> This makes...
>>>>>
>>>>>>  MODULE_DEVICE_TABLE(i2c, st_accel_id_table);
>>>>>
>>>>>
>>>>>
>>>>> ...this table obsolete IIUC. At least that's what I did when switched
>>>>> to ->probe_new() in some drivers.
>>>>>
>>>>> If I'm mistaken (again? :-) ) I would hear from someone to point me
>>>>> how it can be used after a switch.
>>>>
>>>>
>>>>
>>>> It is still used by the i2c-core in i2c_device_match() if DT and ACPI
>>>> matching fails.
>>>
>>>
>>>> And it is used to create the corresponding modaliases for
>>>> driver loading.
>>>
>>>
>>> My question is "How?!"
>>> I don't really see any points to match against it after switching to
>>> ->probe_new().
>>>
>>> Could you point me to the code path in i2c (or OF?) core for that?
>>
>>
>> As written above in i2c-core-base.c: i2c_device_match() ->
>> i2c_match_id(driver->id_table,...
>>
>> This is used for driver matching before probe() or probe_new() of the device
>> driver can be called. probe_new() actually is a function signature change
>> only.
>
> Okay, IIUC we got a match. What should we do with it? The table is not
> used in ->probe_new() (in i2c core), so, you can't say which line
> matched there.

The table is not used by the driver, but is necessary to

a) bind an i2c device declared via i2c_board_info with type field set
    to one of the names of the i2c_device_id table to this driver
b) bind an i2c device declared via DT or ACPI but with no match in of_id/
    acpi_id table but an i2c_device_id table match to this driver (fallback
    matching)
c) create the right modaliases at compile time for this driver to make
    module auto-loading work in case of a) and b)

Niko