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

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Date:	Tue, 05 Apr 2016 12:10:05 -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,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Subject: Re: [PATCH] iommu/rockchip: Fix "is stall active" check

Am Dienstag, 5. April 2016, 18:28:58 schrieb John Keeping:
> 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

So it seems both you and Tomeu were working to resolve the same issue [2].

And John's patch seems to actually fix the underlying problem.


[2] https://lkml.org/lkml/2016/3/22/493


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