linux-kernel - Re: [RFC PATCH 4/6] leds: pca955x: Use pinctrl to map GPIOs to pins

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Message-Id: <96e52916-f113-4a91-b83f-e0de144611ca@www.fastmail.com>
Date:   Wed, 11 Aug 2021 09:49:05 +0930
From:   "Andrew Jeffery" <andrew@...id.au>
To:     "Linus Walleij" <linus.walleij@...aro.org>
Cc:     "Linux LED Subsystem" <linux-leds@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Cédric Le Goater <clg@...d.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Joel Stanley" <joel@....id.au>, "Pavel Machek" <pavel@....cz>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "Linux ARM" <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 4/6] leds: pca955x: Use pinctrl to map GPIOs to pins



On Tue, 10 Aug 2021, at 23:24, Linus Walleij wrote:
> On Fri, Jul 23, 2021 at 9:59 AM Andrew Jeffery <andrew@...id.au> wrote:
> 
> > The leds-pca955x driver currently assumes that the GPIO numberspace and
> > the pin numberspace are the same. This quickly falls apart with a
> > devicetree binding such as the following:
> (...)
> 
> Honestly I do not understand this patch. It seems to implement a pin
> controller and using it in nonstandard ways.

Yeah, it's a bit abusive, hence RFC :)

> 
> If something implements the pin controller driver API it should be
> used as such IMO, externally. This seems to be using it do relay
> calls to itself which seems complicated, just invent something
> locally in the driver in that case? No need to use pin control?

Right. After discussions with Andy I'm going to rework the approach to 
GPIOs which will remove a lot of complexity.

The thought was to try to maintain the intent of the devicetree binding 
and use existing APIs, but all-in-all it's ended up twisting things up 
in knots a fair bit. We discard a lot of it by making the gpiochip 
always cover all pins and track use directly in the driver.

> 
> Can you explain why this LED driver needs to implement a pin
> controller?

The short answer is it doesn't as it has none of the associated 
hardware.

I'll cook up something simpler with the aim to avoid non-standard (or 
any) pinctrl.

Andrew