linux-kernel - Re: [PATCH v2] i2c: i801: Register optional lis3lv02d i2c device on Dell machines

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Date:   Tue, 13 Feb 2018 19:01:37 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Pali Rohár <pali.rohar@...il.com>
Cc:     Jean Delvare <jdelvare@...e.com>, Wolfram Sang <wsa@...-dreams.de>,
        Michał Kępień <kernel@...pniu.pl>,
        Steven Honeyman <stevenhoneyman@...il.com>,
        Valdis Kletnieks <Valdis.Kletnieks@...edu>,
        Jochen Eisinger <jochen@...guin-breeder.org>,
        Gabriele Mazzotta <gabriele.mzt@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Mario Limonciello <Mario_Limonciello@...l.com>,
        Alex Hung <alex.hung@...onical.com>,
        Takashi Iwai <tiwai@...e.de>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>
Subject: Re: [PATCH v2] i2c: i801: Register optional lis3lv02d i2c device on
 Dell machines

On Tue, Feb 13, 2018 at 6:50 PM, Pali Rohár <pali.rohar@...il.com> wrote:
> On Tuesday 13 February 2018 17:06:19 Andy Shevchenko wrote:
>> On Tue, Feb 13, 2018 at 5:00 PM, Pali Rohár <pali.rohar@...il.com> wrote:
>> > On Tuesday 13 February 2018 16:55:00 Andy Shevchenko wrote:
>> >> On Mon, Feb 12, 2018 at 5:30 PM, Pali Rohár <pali.rohar@...il.com> wrote:
>> >> > On Wednesday 31 January 2018 14:27:51 Andy Shevchenko wrote:

>> >> > Following table already exists in dell-smo8800.c file:
>> >> > Can we reuse it?

>> >> >  Maybe moving array smo8800_ids[] into some header file
>> >> > (which one?) and statically inline it?
>> >>
>> >> Bad idea.
>> >>
>> >> > Or having it only in
>> >> > dell-smo8800.c file and exporting its symbol?
>> >>
>> >> Even worse.
>> >>
>> >> > Or is there better idea?
>> >> >
>> >> > For sure I do not want to copy paste this table into another module and
>> >> > maintaining two copies of this list.
>> >>
>> >> The copy is fine. Can you guarantee that those two lists would be
>> >> always the same? I'm not.
>> >
>> > Me neither.
>> >
>> >> And besides that explicitly over implicitly  is a really good thing. I
>> >> would not like to grep for an ID followed by grepping include line and
>> >> check each files to check if it uses it or not.
>> >
>> > So what do you suggest now?
>>
>> Copy'n'paste and maintain two lists.
>> Yes, it's not the ideal, but working solution.
>>
>> You may put a comment before each list to explain what the second does
>> and tell a contributor to look at it and update if needed.
>
> I'm not maintainer of i2c-i801.ko, Jean Delvare & Wolfram Sang are.
> Therefore instructing future contributors would be up to them.

Right. But from ACPI prospective the proposed change is not okay by my opinion.

How can I see what drivers are binding / relying on certain ACPI ID?

More precisely,

% git grep -n -w SMO8800

would be useless until one gets an idea to match against partial strings.

> Jean, it is OK?

>> > Having one file where it would be defined is a bad idea for you.
>>
>> Not just "one file", but "one *header* file". Or "exporting a symbol"
>> which is basically not supposed to be exported.
>> ID tables are part of the actual drivers, neither headers, nor libraries.
>
> But this is exactly what is needed. This ACPI ID table contains ACPI
> names which says if accelerometer is present or not.

In case of dell-smo8800.c the driver actually *binds* to these IDs.
Your change just provide another table to match and answer to the
question if XYZ is present on a such platform or not.

Similar approach is used in spi-pxa2xx.c (check pxa2xx_spi_pci_compound_match).

-- 
With Best Regards,
Andy Shevchenko