Re: [PATCH] gpio: add gpio_of_helper

[Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx>]

Hi Linus,

> On Oct 28, 2014, at 19:09 , Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> 
> On Wed, Oct 22, 2014 at 11:58 AM, Pantelis Antoniou
> <panto@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
>>> On Oct 22, 2014, at 12:41 PM, Alexandre Courbot <gnurou@xxxxxxxxx> wrote:
> 
>>> Pinmux configuration sounds like a job for pinmux more than GPIO, and
>>> exporting potentially many GPIOs to user-space sounds like a work for
>>> a proper driver.
>> 
>> I’m afraid that’s not the case. A great many users (...)
> 
> How many are many? How long is a piece of string? "Many" may
> refer to every system on the market or me and my friends.
> That claim has to be more specific.
> 

On every embedded product board that I have worked on for a customer,
invariably user-space GPIO was required for some odd pieces of hardware.

I guess that’s in the dozen range for me, and Jiri that originally posted
seems to be doing something similar too.

>> do not require anything
>> more than setting a pinmux
> 
> Which can be done (from device tree if need be) using pin control
> hogs.
> 

>> and the GPIO configuration (input/output).
> 
> And we have GPIO hogs for that in the pipe.
> 

The original proposal was on January, and there’s a RFC posted just a few days back.
I will take a look.

>> They can then do low speed I/O using the sysfs interface, without having to
>> use any complex APIs (shell works just fine).
> 
> So what is added is export capability, which could be done by supplanting
> the GPIO hogging mechanism with some linux,export thing.
> 

Yes, that would be nice.

>> Think of stuff like controlling a sprinkler valve, or something like a mechanical
>> door detection open state.
> 
> OK it's in the department of automatic control, which is arguably the
> only technical area where userspace GPIO handling actually makes
> sense.
> 

Err, let’s just say that I completely disagree, but whatever.

If the new GPIO hogging methods make it in mainline along with the export
mechanism it’d be fine by me.

> Yours,
> Linus Walleij

Regards

— Pantelis

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