Subject: [PATCH] iommu/arm-smmu: don't touch the secure STLBIALL register

From: [email-masked] (Will Deacon)
Date: Wed, 7 Jan 2015 18:53:22 +0000

On Wed, Jan 07, 2015 at 06:35:41PM +0000, Mitchel Humpherys wrote:
> On Wed, Jan 07 2015 at 10:04:20 AM, Will Deacon <[email-masked]> wrote:
> > On Wed, Jan 07, 2015 at 05:52:46PM +0000, Mitchel Humpherys wrote:
> >> On Wed, Jan 07 2015 at 02:13:00 AM, Will Deacon <[email-masked]> wrote:
> >> > If would be better to check for the ARM_SMMU_OPT_SECURE_CFG_ACCESS feature
> >> > and, if it's set then zero ARM_SMMU_GR0_STLBIALL at the correct address
> >> > otherwise do the ARM_SMMU_GR0_TLBIALLH and ARM_SMMU_GR0_TLBIALLNSNH.
> >> 
> >> I'm confused.  The problem I'm addressing here is that we're touching a
> >> register that's marked as "secure only", which causes our system to
> >> crash.  Why would we ever want to touch a secure only register, calxeda
> >> workaround or not?
> >
> > Because I think the way the SMMU is wired for Calxeda is that the CPU can
> > only see the secure side of the register interface, so the only way to nuke
> > the whole TLB would be to use ARM_SMMU_GR0_STLBIALL.
> 
> Still not sure I understand what "the correct address" is for STLBIALL
> on Calxeda (i.e. whether or not we need to use ARM_SMMU_GR0_NS), but
> something like:

Hehe, I wasn't actually expecting a patch, but thanks!

> -- >8 --
> Subject: [PATCH v2] iommu/arm-smmu: don't touch the secure STLBIALL register
> 
> Currently we do a STLBIALL when we initialize the SMMU.  However, on
> systems with sane secure
> configurations (i.e. !ARM_SMMU_OPT_SECURE_CFG_ACCESS) that register is
> not supposed to be touched and is marked as "Secure only" in the spec.
> Touching it results in a crash on those platforms.  However, on
> platforms with ARM_SMMU_OPT_SECURE_CFG_ACCESS it's the only way to nuke
> the whole TLB, so leave it in for them but rip it out for everyone else.
> 
> Signed-off-by: Mitchel Humpherys <[email-masked]>
> ---
>  drivers/iommu/arm-smmu.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 60558f794922..d4c149d83f3d 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1686,9 +1686,12 @@ static void arm_smmu_device_reset(struct arm_smmu_device *smmu)
>  	}
>  
>  	/* Invalidate the TLB, just in case */
> -	writel_relaxed(0, gr0_base + ARM_SMMU_GR0_STLBIALL);
> -	writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLH);
> -	writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLNSNH);
> +	if (smmu->options & ARM_SMMU_OPT_SECURE_CFG_ACCESS) {
> +		writel_relaxed(0, gr0_base + ARM_SMMU_GR0_STLBIALL);

Right, so this is the bit where we'd need some Calxeda information about
whether or not to subtract 0x400 from gr0_base or not.

> +	} else {
> +		writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLH);
> +		writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLNSNH);
> +	}

For now, I've applied your original patch pending any insight on the above.

Cheers,

Will