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

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Date:   Wed, 4 Jul 2018 13:19:26 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Nikolaus Voss <nikolaus.voss@...wensteinmedical.de>,
        Javier Martinez Canillas <javierm@...hat.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()

Summon Javier to the discussion.
For my opinion he is an expert in this topic.

On Wed, Jul 4, 2018 at 12:42 PM, Nikolaus Voss
<nikolaus.voss@...wensteinmedical.de> wrote:
> 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)

Javier, just a summary of the above. Nikolaus switched one driver to
use ->probe_new() hook and left i2c ID table at the same time.
My understanding that this table is not anymore in use.

But I have to admit I didn't see entire picture of this. Can you shed a light?

-- 
With Best Regards,
Andy Shevchenko