linux-kernel - Re: [PATCH] ACPI / gpio: avoid warning for gpio hogging code

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Date:   Wed, 9 Nov 2016 09:44:41 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Alexandre Courbot <gnurou@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        Christophe Ricard <christophe.ricard@...il.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI / gpio: avoid warning for gpio hogging code

On Tue, Nov 8, 2016 at 2:40 PM, Arnd Bergmann <arnd@...db.de> wrote:

> The newly added acpi_gpiochip_scan_gpios function produces a few harmless
> warnings:
>
> drivers/gpio/gpiolib-acpi.c: In function ‘acpi_gpiochip_add’:
> drivers/gpio/gpiolib-acpi.c:925:7: error: ‘dflags’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/gpio/gpiolib-acpi.c:925:9: error: ‘lflags’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> The problem is that he compiler cannot know that a negative return value
> from fwnode_property_read_u32_array() or acpi_gpiochip_pin_to_gpio_offset()
> implies that the IS_ERR(gpio_desc) is true, as the value could in theory
> be below -MAX_ERRNO.
>
> The function already initializes its output values to zero, and moving
> that intialization a little higher up ensures that we can never have
> uninitialized data in the caller.
>
> Fixes: c80f1ba75df2 ("ACPI / gpio: Add hogging support")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Patch applied with Mika's ACK.

Yours,
Linus Walleij