Re: [PATCH 7/7] iommu/arm-smmu: Clear global and context bank fault status and syndrome registers

[Andreas Herrmann <andreas.herrmann-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org>]

On Wed, Sep 25, 2013 at 12:49:18PM -0400, Will Deacon wrote:
> On Tue, Sep 24, 2013 at 07:32:47PM +0100, Andreas Herrmann wrote:
> > On Tue, Sep 24, 2013 at 11:42:52AM -0400, Will Deacon wrote:
> > > On Tue, Sep 24, 2013 at 04:07:01PM +0100, Andreas Herrmann wrote:
> > > > Signed-off-by: Andreas Herrmann <andreas.herrmann-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org>
> > > > ---
> > > >  drivers/iommu/arm-smmu.c |    9 +++++++++
> > > >  1 file changed, 9 insertions(+)
> > > > 
> > > > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> > > > index 251564e..a499146 100644
> > > > --- a/drivers/iommu/arm-smmu.c
> > > > +++ b/drivers/iommu/arm-smmu.c
> > > > @@ -645,6 +645,10 @@ static void arm_smmu_init_context_bank(struct arm_smmu_domain *smmu_domain)
> > > >  	stage1 = root_cfg->cbar != CBAR_TYPE_S2_TRANS;
> > > >  	cb_base = ARM_SMMU_CB_BASE(smmu) + ARM_SMMU_CB(smmu, root_cfg->cbndx);
> > > >  
> > > > +	/* clear fsr */
> > > > +	writel_relaxed(0xffffffff, cb_base + ARM_SMMU_CB_FSR);
> > > > +	writel_relaxed(0, cb_base + ARM_SMMU_CB_FSYNR0);
> > > > +
> > > >  	/* CBAR */
> > > >  	reg = root_cfg->cbar;
> > > >  	if (smmu->version == 1)
> > > > @@ -1570,6 +1574,11 @@ static void arm_smmu_device_reset(struct arm_smmu_device *smmu)
> > > >  	int i = 0;
> > > >  	u32 scr0 = readl_relaxed(gr0_base + ARM_SMMU_GR0_sCR0);
> > > >  
> > > > +	/* clear global FSRs */
> > > > +	writel(0xffffffff, gr0_base + ARM_SMMU_GR0_sGFSR);
> > > > +	writel(0, gr0_base + ARM_SMMU_GR0_sGFSYNR0);
> > > > +	writel(0, gr0_base + ARM_SMMU_GR0_sGFSYNR1);
> > > 
> > > Why do you need this?
> > 
> > According to the spec the status and syndrome registers have
> > unknown/unpredictable reset values. So better set known values before
> > we start to use these registers (ie. handle faults where we read
> > them). No?
> 
> Sure, but the only time these are made visible should be if we take a fault,
> in which case the registers should contain something meaningful. I guess I
> could see a problem if there is a shared interrupt line for faults though,
> so a cut-down version of your patch (just clearing ARM_SMMU_GR0_sGFSR and
> the ARM_SMMU_CB_FSR registers) should be enough.

Agreed.

Andreas