linux-kernel - Re: [PATCH] gpio: zynq: Setup chip->base based on alias ID

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Date:   Wed, 2 May 2018 12:10:32 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michal Simek <monstr@...str.eu>,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>,
        Peter Crosthwaite <peter.crosthwaite@...inx.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Rob Herring <robherring2@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] gpio: zynq: Setup chip->base based on alias ID

On Thu, Apr 26, 2018 at 3:35 PM, Michal Simek <michal.simek@...inx.com> wrote:

>> The only use case which I can think about is userspace sysfs
>> and then I would really like to know why these userspace
>> users cannot use the character device that is nowadays
>> supported by libgpiod and there is even patches for some
>> IoT libraries to use it. The character device makes the
>> GPIO Linux "base" irrelevant for userspace.
>>
>> GPIO sysfs is deprecated and moved to the obsolete ABI.
>>
>> If there are legacy applications that use this I would have
>> to consider it, but since this has been -1 since the driver
>> was merged I find that unlikely.
>
> Yes, it is about legacy application which I have seen recently and there
> is no source code for application calls it because board vendor doesn't
> provide it.
>
> You are right that -1 was used from the beginning in mainline but
> unfortunately this driver was in vendor tree for a while and it uses 0
> there.
>
> In upstreaming this was changed to -1 but customers have a lot of code
> which developed against vendor tree and they want to use
> latest&greatest. And without this they are not able to run that
> applications.
>
> I found that this logic is already in 5 drivers in mainline that's why I
> send this patch to be +1.

I see.

Sadly comaptibility with out-of-tree driver code is none of our
(community) business.

We do pay a lot of effort not to break the ABI to userspace, but
it needs to be an ABI coming from the mainline kernel, not from
a vendor tree.

So to the mainline kernel this is no regression.

Yours,
Linus Walleij