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

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Message-Id: <a42db25f-33af-4232-9acd-815f7b116c71@www.fastmail.com>
Date:   Thu, 03 Mar 2022 11:00:11 +1030
From:   "Andrew Jeffery" <andrew@...id.au>
To:     "Pavel Machek" <pavel@....cz>, "Joel Stanley" <joel@....id.au>
Cc:     "Linus Walleij" <linus.walleij@...aro.org>,
        Cédric Le Goater <clg@...d.org>,
        linux-leds@...r.kernel.org,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "Rob Herring" <robh+dt@...nel.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 Wed, 2 Mar 2022, at 19:24, Pavel Machek wrote:
> Hi!
>
>> > > 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!
>> >
>> > This is simpler than the 'ngpio' business we had before.
>> >
>> > Reviewed-by: Cédric Le Goater <clg@...d.org>
>> 
>> I saw that you recently merged some LED patches. I was wondering if
>> you could consider this series for v5.18. It still applies cleanly,
>> and we've been running it for a while now, so it's very well tested.
>
> Thanks, applied. I must say this is really ninja-mutant driver, but I
> see no better way.
>
> +++ b/drivers/leds/leds-pca955x.c
> @@ -429,7 +429,7 @@ pca955x_get_pdata(struct i2c_client *client, struct 
> pca955x_chipdef *chip)
>         int count;
>
> This really should be unsigned. Care to fix/submit a patch?

I'll send a fix.

Andrew