linux-kernel - Re: [PATCH] pwm: meson: handle unknown ID values

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Date:   Tue, 6 Sep 2016 14:55:48 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>, linux-pwm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pwm: meson: handle unknown ID values

On 09/06/2016 02:50 PM, Arnd Bergmann wrote:
> When building with -Wmaybe-uninitialized, we get a couple of harmless
> warnings about three functions in this new driver that don't look
> safe to the compiler:
> 
> drivers/pwm/pwm-meson.c: In function 'meson_pwm_get_state':
> drivers/pwm/pwm-meson.c:355:26: error: 'mask' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/pwm/pwm-meson.c: In function 'meson_pwm_disable':
> drivers/pwm/pwm-meson.c:263:13: error: 'enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/pwm/pwm-meson.c: In function 'meson_pwm_apply':
> drivers/pwm/pwm-meson.c:231:13: error: 'clk_shift' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/pwm/pwm-meson.c:231:36: error: 'enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/pwm/pwm-meson.c:231:24: error: 'clk_enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> Specifically, if we have a device with an id other than 0 or 1,
> this would result in undefined behavior. This is currently not
> possible, but the compiler cannot be expected to know this.
> 
> This patch adds a 'default' clause to let the compiler know
> what to do instead, which shuts up the warning and makes the
> code slightly more resiliant in case it gets extended to other
> identifiers.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/pwm/pwm-meson.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
> index 566f5cb81021..25abd95dcc7b 100644
> --- a/drivers/pwm/pwm-meson.c
> +++ b/drivers/pwm/pwm-meson.c
> @@ -242,6 +242,9 @@ static void meson_pwm_enable(struct meson_pwm *meson,
>  		clk_enable = MISC_B_CLK_EN;
>  		enable = MISC_B_EN;
>  		break;
> +
> +	default:
> +		return;
>  	}
>  
>  	value = readl(meson->base + REG_MISC_AB);
> @@ -270,6 +273,9 @@ static void meson_pwm_disable(struct meson_pwm *meson, unsigned int id)
>  	case 1:
>  		enable = MISC_B_EN;
>  		break;
> +
> +	default:
> +		return;
>  	}
>  
>  	value = readl(meson->base + REG_MISC_AB);
> @@ -349,6 +355,10 @@ static void meson_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
>  	case 1:
>  		mask = MISC_B_EN;
>  		break;
> +
> +	default:
> +		state->enabled = 0;
> +		return;
>  	}
>  
>  	value = readl(meson->base + REG_MISC_AB);
> 

Acked-by: Neil Armstrong <narmstrong@...libre.com>