Re: [PATCH] mmc: sdhci-cadence: Fix -Wuninitialized in sdhci_cdns_tune_blkgap()

["Benoît Monin" <benoit.monin@bootlin.com>]

Hi Nathan,

On Tuesday, 19 August 2025 at 19:28:49 CEST, Nathan Chancellor wrote:
> Clang warns (or errors with CONFIG_WERROR=y):
> 
>   drivers/mmc/host/sdhci-cadence.c:297:9: error: variable 'hrs37_mode' is uninitialized when used here [-Werror,-Wuninitialized]
>     297 |         writel(hrs37_mode, hrs37_reg);
>         |                ^~~~~~~~~~
>   drivers/mmc/host/sdhci-cadence.c:291:16: note: initialize the variable 'hrs37_mode' to silence this warning
>     291 |         u32 hrs37_mode;
>         |                       ^
>         |                        = 0
> 
> A previous revision assigned SDHCI_CDNS_HRS37_MODE_MMC_HS200 to
> hrs37_mode in a switch statement but the final revision moved to a
> simple if statement. Pass that as the value to writel() and
> remove hrs37_mode, clearing up the warning.
> 
> Fixes: 60613a8b9b81 ("mmc: sdhci-cadence: implement multi-block read gap tuning")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  drivers/mmc/host/sdhci-cadence.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-cadence.c b/drivers/mmc/host/sdhci-cadence.c
> index a2a4a5b0ab96..eaa88897a256 100644
> --- a/drivers/mmc/host/sdhci-cadence.c
> +++ b/drivers/mmc/host/sdhci-cadence.c
> @@ -288,13 +288,12 @@ static int sdhci_cdns_tune_blkgap(struct mmc_host *mmc)
>  	void __iomem *hrs38_reg = priv->hrs_addr + SDHCI_CDNS_HRS38;
>  	int ret;
>  	u32 gap;
> -	u32 hrs37_mode;
>  
>  	/* Currently only needed in HS200 mode */
>  	if (host->timing != MMC_TIMING_MMC_HS200)
>  		return 0;
>  
> -	writel(hrs37_mode, hrs37_reg);
> +	writel(SDHCI_CDNS_HRS37_MODE_MMC_HS200, hrs37_reg);
>  
>  	for (gap = 0; gap <= SDHCI_CDNS_HRS38_BLKGAP_MAX; gap++) {
>  		writel(gap, hrs38_reg);
> 
Thanks for the catch!

I don't get how gcc does not raise a warning here, only clang does. I
did build with gcc-11 and gcc-15 and they don't complain about this
uninitialized variable.

Tested-by: Benoît Monin <benoit.monin@bootlin.com>

> ---
> base-commit: 7138017038c42feb682445407974ed736e1ff308
> change-id: 20250819-mmc-sdhci-cadence-fix-uninit-hrs37_mode-cc1246cb39d8
> 
> Best regards,
> --  
> Nathan Chancellor <nathan@kernel.org>
> 
> 

Best regards,
-- 
Benoît Monin, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com