Re: [PATCH] clk: lpc32xx: fix compilation warning

[Vladimir Zapolskiy <vz@mleia.com>]

Hi Sylvain,

On 22.02.2016 20:49, slemieux.tyco@gmail.com wrote:
> From: Sylvain Lemieux <slemieux@tycoint.com>
> 
> This patch remove the following compilation warning:
> - drivers/clk/nxp/clk-lpc32xx.c: In function 'lpc32xx_clk_register':
>   warning: 'hw' may be used uninitialized in this function [-Wmaybe-uninitialized]
> - drivers/clk/nxp/clk-lpc32xx.c: In function 'clk_hclk_pll_round_rate':
>   warning: 'p' may be used uninitialized in this function [-Wmaybe-uninitialized]
>   warning: 'n' may be used uninitialized in this function [-Wmaybe-uninitialized]
>   warning: 'm' may be used uninitialized in this function [-Wmaybe-uninitialized]

All warnings are false positives, please explicitly mention this in the commit message.

> Tested using gcc version 4.7.3.
> 
> Signed-off-by: Sylvain Lemieux <slemieux@tycoint.com>
> ---
>  drivers/clk/nxp/clk-lpc32xx.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/nxp/clk-lpc32xx.c b/drivers/clk/nxp/clk-lpc32xx.c
> index 48b3a11..331f91b 100644
> --- a/drivers/clk/nxp/clk-lpc32xx.c
> +++ b/drivers/clk/nxp/clk-lpc32xx.c
> @@ -13,6 +13,7 @@
>  #include <linux/clk-provider.h>
>  #include <linux/of_address.h>
>  #include <linux/regmap.h>
> +#include <linux/compiler-gcc.h>
>  
>  #include <dt-bindings/clock/lpc32xx-clock.h>
>  
> @@ -588,7 +589,8 @@ static long clk_hclk_pll_round_rate(struct clk_hw *hw, unsigned long rate,
>  				    unsigned long *parent_rate)
>  {
>  	struct lpc32xx_pll_clk *clk = to_lpc32xx_pll_clk(hw);
> -	u64 m_i, m, n, p, o = rate, i = *parent_rate, d = (u64)rate << 6;
> +	u64 m_i, o = rate, i = *parent_rate, d = (u64)rate << 6;
> +	u64 uninitialized_var(m), uninitialized_var(n), uninitialized_var(p);

I think that dummy initialization is good enough here, i.e. assigning
the variables to 0, AFAIU that's a common way to deal with compiler's false
positives, usage of uninitialized_var() looks exotic.

>  	int p_i, n_i;
>  
>  	pr_debug("%s: %lu/%lu\n", clk_hw_get_name(hw), *parent_rate, rate);
> @@ -1414,7 +1416,7 @@ static struct clk * __init lpc32xx_clk_register(u32 id)
>  			.flags = lpc32xx_clk->flags,
>  			.ops = clk_hw->hw0.ops,
>  		};
> -		struct clk_hw *hw;
> +		struct clk_hw *uninitialized_var(hw);

Same as above, struct clk_hw *hw = NULL would be good enough here.

>  		if (clk_hw->type == CLK_LPC32XX)
>  			hw = &clk_hw->hw0.clk.hw;
> 

--
With best wishes,
Vladimir