[PATCH v2] drm/panel: himax-hx8279: Always initialize goa_{even,odd}_valid in hx8279_check_goa_config()

[Neil Armstrong]

On 23/04/2025 19:41, Nathan Chancellor wrote:
> Clang warns (or errors with CONFIG_WERROR=y):
> 
>    drivers/gpu/drm/panel/panel-himax-hx8279.c:838:6: error: variable 'goa_even_valid' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>      838 |         if (num_zero == ARRAY_SIZE(desc->goa_even_timing))
>          |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    drivers/gpu/drm/panel/panel-himax-hx8279.c:842:23: note: uninitialized use occurs here
>      842 |         if (goa_odd_valid != goa_even_valid)
>          |                              ^~~~~~~~~~~~~~
>    drivers/gpu/drm/panel/panel-himax-hx8279.c:838:2: note: remove the 'if' if its condition is always true
>      838 |         if (num_zero == ARRAY_SIZE(desc->goa_even_timing))
>          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>      839 |                 goa_even_valid = false;
>    drivers/gpu/drm/panel/panel-himax-hx8279.c:818:36: note: initialize the variable 'goa_even_valid' to silence this warning
>      818 |         bool goa_odd_valid, goa_even_valid;
>          |                                           ^
>          |                                            = 0
> 
> Even though only the even valid variable gets flagged, both valid
> variables appear to have the same issue of possibly being used
> uninitialized if the if statement initializing them to false is not
> taken.
> 
> Turn the if statement then variable assignment into a single variable
> assignment, which states that the configuration is valid when there are
> not all zeros, clearing up the warning since the variable will always be
> initialized.
> 
> Fixes: 38d42c261389 ("drm: panel: Add driver for Himax HX8279 DDIC panels")
> Suggested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
> Signed-off-by: Nathan Chancellor <nathan at kernel.org>
> ---
> Changes in v2:
> - Initialize valid variables once using the inverse of the current
>    condition (Angelo).
> - Link to v1: https://lore.kernel.org/r/20250422-panel-himax-hx8279-fix-sometimes-uninitialized-v1-1-614dba12b30d@kernel.org
> ---
>   drivers/gpu/drm/panel/panel-himax-hx8279.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-himax-hx8279.c b/drivers/gpu/drm/panel/panel-himax-hx8279.c
> index b48b350b62da..fb302d1f91b9 100644
> --- a/drivers/gpu/drm/panel/panel-himax-hx8279.c
> +++ b/drivers/gpu/drm/panel/panel-himax-hx8279.c
> @@ -825,8 +825,7 @@ static int hx8279_check_goa_config(struct hx8279 *hx, struct device *dev)
>   			num_zero++;
>   	}
>   
> -	if (num_zero == ARRAY_SIZE(desc->goa_odd_timing))
> -		goa_odd_valid = false;
> +	goa_odd_valid = (num_zero != ARRAY_SIZE(desc->goa_odd_timing));
>   
>   	/* Up to 3 zeroes is a valid config. Check them all. */
>   	num_zero = 1;
> @@ -835,8 +834,7 @@ static int hx8279_check_goa_config(struct hx8279 *hx, struct device *dev)
>   			num_zero++;
>   	}
>   
> -	if (num_zero == ARRAY_SIZE(desc->goa_even_timing))
> -		goa_even_valid = false;
> +	goa_even_valid = (num_zero != ARRAY_SIZE(desc->goa_even_timing));
>   
>   	/* Programming one without the other would make no sense! */
>   	if (goa_odd_valid != goa_even_valid)
> 
> ---
> base-commit: dcbd5dcc956e2331414fd7020b4655df08deeb87
> change-id: 20250422-panel-himax-hx8279-fix-sometimes-uninitialized-207354fb930c
> 
> Best regards,

Reviewed-by: Neil Armstrong <neil.armstrong at linaro.org>