linux-kernel - Re: [PATCH] phy: exynos-mipi-video: avoid uninitialized variable use

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Date:	Wed, 11 May 2016 20:51:55 +0200
From:	Krzysztof Kozlowski <k.kozlowski.k@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Kishon Vijay Abraham I <kishon@...com>,
	Kukjin Kim <kgene@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH] phy: exynos-mipi-video: avoid uninitialized variable use

On Wed, May 11, 2016 at 02:49:53PM +0200, Arnd Bergmann wrote:
> A rework of the exynos-mipi-video driver caused a warning
> about the new __set_phy_state function potentially accessing
> a variable before its initialization:
> 
> drivers/phy/phy-exynos-mipi-video.c: In function '__set_phy_state':
> drivers/phy/phy-exynos-mipi-video.c:238:13: error: 'val' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>   return val & data->resetn_val;
>          ~~~~^~~~~~~~~~~~~~~~~~
> drivers/phy/phy-exynos-mipi-video.c:235:6: note: 'val' was declared here
>   u32 val;
> 
> The failure scenario here is the offset passed into a the
> stub regmap_read() function that does not modify its output,
> however regmap_read() can also fail for other reasons, so
> adding error handling (in this case, returning zero from
> is_running) seems the best solution.
> 
> Note that this warning showed up with the ARM s5pv210_defconfig,
> indicating that we most likely want to either enable CONFIG_REGMAP
> in that defconfig as well, or disable the phy-exynos-mipi-video
> driver.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Fixes: 97a3042f7616 ("phy: exynos-mipi-video: Rewrite handling of phy registers")
> ---
>  drivers/phy/phy-exynos-mipi-video.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/phy/phy-exynos-mipi-video.c b/drivers/phy/phy-exynos-mipi-video.c
> index cc093ebfda94..8b851f718123 100644
> --- a/drivers/phy/phy-exynos-mipi-video.c
> +++ b/drivers/phy/phy-exynos-mipi-video.c
> @@ -233,8 +233,12 @@ static inline int __is_running(const struct exynos_mipi_phy_desc *data,
>  			struct exynos_mipi_video_phy *state)
>  {
>  	u32 val;

Other way would be to initialize val=0 since there is no real error code
returned. Anyway:

Reviewed-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>

Best regards,
Krzysztof

> +	int ret;
> +
> +	ret = regmap_read(state->regmaps[data->resetn_map], data->resetn_reg, &val);
> +	if (ret)
> +		return 0;
>  
> -	regmap_read(state->regmaps[data->resetn_map], data->resetn_reg, &val);
>  	return val & data->resetn_val;
>  }
>  
> -- 
> 2.7.0
> 
> --
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