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

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Date:   Wed, 2 May 2018 12:15:48 +0200
From:   Michal Simek <michal.simek@...inx.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        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 2.5.2018 12:10, Linus Walleij wrote:
> 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.

I understand your statement. On the other hand it is feature which was
permitted in past for some drivers and this is +1.

Thanks,
Michal