linux-kernel - Re: [PATCH 0/2] leds: pca955x: Expose GPIOs for all pins

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Date:   Fri, 24 Sep 2021 03:49:01 +0000
From:   Joel Stanley <joel@....id.au>
To:     Andrew Jeffery <andrew@...id.au>
Cc:     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>, Pavel Machek <pavel@....cz>,
        Linus Walleij <linus.walleij@...aro.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH 0/2] leds: pca955x: Expose GPIOs for all pins

On Tue, 21 Sept 2021 at 04:39, Andrew Jeffery <andrew@...id.au> wrote:
>
> Hello,
>
> This is a rework of a Rube Goldberg-inspired RFC I posted previously:
>
> https://lore.kernel.org/lkml/20210723075858.376378-1-andrew@aj.id.au/
>
> This time around there's a lot less Rube - the series:
>
> 1. Contains no (ab)use of pinctrl
> 2. Always exposes all pins as GPIOs
> 3. Internally tracks the active pins
>
> Without these patches the driver limits the number of pins exposed on
> the gpiochip to the number of pins specified as GPIO in the devicetree,
> but doesn't map between the GPIO and pin number spaces. The result is
> that specifying offset or interleaved GPIOs in the devicetree gives
> unexpected behaviour in userspace.
>
> By always exposing all pins as GPIOs the patches resolve the lack of
> mapping between GPIO offsets and pins on the package in the driver by
> ensuring we always have a 1-to-1 mapping.
>
> The issue is primarily addressed by patch 1/2. Patch 2/2 makes it
> possible to not expose any pins as LEDs (and therefore make them all
> accessible as GPIOs). This has a follow-on effect of allowing the driver
> to bind to a device instantiated at runtime without requiring a
> description in the devicetree.
>
> I've tested the series under qemu to inspect the various interactions
> between LEDs vs GPIOs as well as conflicting GPIO requests.
>
> Please review!

Reviewed-by: Joel Stanley <joel@....id.au>

Cheers,

Joel