linux-kernel - Re: [PATCH] iommu/rockchip: Fix "is stall active" check

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Message-ID: <5389576.zuTxjFsmO4@phil>
Date:	Tue, 05 Apr 2016 10:21:27 -0700
From:	Heiko Stuebner <heiko@...ech.de>
To:	John Keeping <john@...anate.com>
Cc:	Joerg Roedel <joro@...tes.org>, iommu@...ts.linux-foundation.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/rockchip: Fix "is stall active" check

Am Dienstag, 5. April 2016, 15:05:46 schrieb John Keeping:
> Since commit cd6438c5f844 ("iommu/rockchip: Reconstruct to support multi
> slaves") rk_iommu_is_stall_active() always returns false because the
> bitwise AND operates on the boolean flag promoted to an integer and a
> value that is either zero or BIT(2).
> 
> Explicitly convert the right-hand value to a boolean so that both sides
> are guaranteed to be either zero or one.
> 
> rk_iommu_is_paging_enabled() does not suffer from the same problem since
> RK_MMU_STATUS_PAGING_ENABLED is BIT(0), but let's apply the same change
> for consistency and to make it clear that it's correct without needing
> to lookup the value.
> 
> Fixes: cd6438c5f844 ("iommu/rockchip: Reconstruct to support multi
> slaves") Signed-off-by: John Keeping <john@...anate.com>

Nice catch, thanks.

Reviewed-by: Heiko Stuebner <heiko@...ech.de>

John, out of curiosity, how did you find that problem? Excess stall error 
messages or something else?


Thanks
Heiko

> ---
>  drivers/iommu/rockchip-iommu.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/rockchip-iommu.c
> b/drivers/iommu/rockchip-iommu.c index a6f593a0a29e..5710a06c3049 100644
> --- a/drivers/iommu/rockchip-iommu.c
> +++ b/drivers/iommu/rockchip-iommu.c
> @@ -315,8 +315,8 @@ static bool rk_iommu_is_stall_active(struct rk_iommu
> *iommu) int i;
> 
>  	for (i = 0; i < iommu->num_mmu; i++)
> -		active &= rk_iommu_read(iommu->bases[i], RK_MMU_STATUS) &
> -					RK_MMU_STATUS_STALL_ACTIVE;
> +		active &= !!(rk_iommu_read(iommu->bases[i], RK_MMU_STATUS) &
> +					   RK_MMU_STATUS_STALL_ACTIVE);
> 
>  	return active;
>  }
> @@ -327,8 +327,8 @@ static bool rk_iommu_is_paging_enabled(struct rk_iommu
> *iommu) int i;
> 
>  	for (i = 0; i < iommu->num_mmu; i++)
> -		enable &= rk_iommu_read(iommu->bases[i], RK_MMU_STATUS) &
> -					RK_MMU_STATUS_PAGING_ENABLED;
> +		enable &= !!(rk_iommu_read(iommu->bases[i], RK_MMU_STATUS) &
> +					   RK_MMU_STATUS_PAGING_ENABLED);
> 
>  	return enable;
>  }