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

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Date:	Tue, 5 Apr 2016 18:28:58 +0100
From:	John Keeping <john@...anate.com>
To:	Heiko Stuebner <heiko@...ech.de>
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

On Tue, 05 Apr 2016 10:21:27 -0700, Heiko Stuebner wrote:

> 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?

I was testing the drm iommu patches I posted today [1] and noticed an
"Enable stall request timed out" error when unbinding the
display-subsystem, but the RK_MMU_STATUS value printed in the error
message indicated that stall active was set.

[1] http://article.gmane.org/gmane.comp.video.dri.devel/150721

> > ---
> >  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;
> >  }  
>