linux-kernel - Re: [PATCH 0/5] pinctrl_gpio_get

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Message-ID: <CAHp75VfPVB6BwkL1+bGRsi03g6io0A0Cty+ykSDkYevOvq=VGA@mail.gmail.com>
Date:   Fri, 29 Jun 2018 18:29:45 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/5] pinctrl_gpio_get_direction & ingenic fixes

On Thu, Jun 28, 2018 at 10:11 PM, Paul Cercueil <paul@...pouillou.net> wrote:
> Le mer. 27 juin 2018 à 19:18, Andy Shevchenko <andy.shevchenko@...il.com> a
> écrit :
>> On Wed, Jun 27, 2018 at 2:48 PM, Paul Cercueil <paul@...pouillou.net>
>> wrote:

>> I dunno what Linus would going to say about this, but I would like to
>> see a schematics for this piece of IP.

> ftp://ftp.ingenic.com/SOC/JZ4780/JZ4780_pm.pdf

I'm not sure you referred to a proper document "Mobile Application
Processor. Programming Manual"

I didn't find quickly what I'm looking for. Care to point me out to
the page number?
Thanks!

>> Even if GPIO and pin muxing has only one set of buffers to indicate
>> input or output (same registers in use) it's a GPIO driver business to
>> get direction from GPIO part of IP.
>
>
> If I follow that logic it's also a GPIO driver business to set the direction
> of a GPIO, right? Truth is the pinctrl subsystem takes care of that. So why
> have "set direction" and no "get direction"?

Because it's a pin muxing business depending on the function chosen.

It solely depends on a schematic. For the example, everyone knows that
MOSI is out always, otherwise SPI function would not work.
.get_direction() has useful meaning only for GPIO function. (This is
my understanding from electrical configuration of buffers).

>> Looking into the existing code I would rather say that
>> pinctrl-ingenic.c should incorporate gpio-ingenic.c as they are
>> (partially) sharing same registers.
>> To ->get_direction() implementation it's pretty straight forward, just
>> read necessary registers in the gpio-ingenic.c directly. No need to
>> have pin control or pin muxing to be involved.

> Sure, it'd be pretty straightforward to do it from the GPIO driver, but I'd
> still like to hear Linus' point of view about this.

Sure.

> As for merging pinctrl-ingenic.c and gpio-ingenic.c... I wouldn't disagree
> more,
> even if they share registers, they belong to different subsystems. Besides,
> your platform might need the pinctrl driver but not the GPIO one, or you
> might
> want to provide the GPIO driver as a loadable module, etc.

It was just my observation, I'm not a maintainer of that code  nor
author, so, up to you how to proceed.

-- 
With Best Regards,
Andy Shevchenko