linux-kernel - Re: [PATCH v2] iommu: arm-smmu-v3: Mark expected switch fall-through

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Date:   Tue, 30 Jul 2019 16:26:01 +0100
From:   Will Deacon <will@...nel.org>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     joro@...tes.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        robin.murphy@....com
Subject: Re: [PATCH v2] iommu: arm-smmu-v3: Mark expected switch fall-through

On Tue, Jul 30, 2019 at 05:20:11PM +0200, Anders Roxell wrote:
> Now that -Wimplicit-fallthrough is passed to GCC by default, the
> following warning shows up:
> 
> ../drivers/iommu/arm-smmu-v3.c: In function ‘arm_smmu_write_strtab_ent’:
> ../drivers/iommu/arm-smmu-v3.c:1189:7: warning: this statement may fall
>  through [-Wimplicit-fallthrough=]
>     if (disable_bypass)
>        ^
> ../drivers/iommu/arm-smmu-v3.c:1191:3: note: here
>    default:
>    ^~~~~~~
> 
> Rework so that the compiler doesn't warn about fall-through. Make it
> clearer by calling 'BUG_ON()' when disable_bypass is set, and always
> 'break;'
> 
> Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> ---
>  drivers/iommu/arm-smmu-v3.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index a9a9fabd3968..c5c93e48b4db 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -1186,8 +1186,8 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
>  			ste_live = true;
>  			break;
>  		case STRTAB_STE_0_CFG_ABORT:
> -			if (disable_bypass)
> -				break;
> +			BUG_ON(!disable_bypass);
> +			break;
>  		default:
>  			BUG(); /* STE corruption */
>  		}
> -- 
> 2.20.1

Acked-by: Will Deacon <will@...nel.org>

Joerg -- if you'd like to pick this up as a fix, feel free, otherwise I'll
include it in my pull request for 5.4.

Cheers,

Will