[PATCH] iommu/arm-smmu-v3: Implement shutdown method

On 6/29/2017 2:34 PM, Will Deacon wrote:

On Thu, Jun 29, 2017 at 01:40:15PM -0400, Nate Watterson wrote:

quoted

The shutdown method disables the SMMU and its interrupts to avoid
potentially corrupting a new kernel started with kexec.

Signed-off-by: Nate Watterson <redacted>
---
  drivers/iommu/arm-smmu-v3.c | 11 +++++++++++
  1 file changed, 11 insertions(+)

We should update arm-smmu.c as well.

quoted

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 380969a..907d576 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c

@@ -2765,9 +2765,19 @@ static int arm_smmu_device_remove(struct platform_device *pdev)
  	struct arm_smmu_device *smmu = platform_get_drvdata(pdev);
  
  	arm_smmu_device_disable(smmu);
+
+	/* Disable IRQs */
+	arm_smmu_write_reg_sync(smmu, 0, ARM_SMMU_IRQ_CTRL,
+				ARM_SMMU_IRQ_CTRLACK);
+

Can you justify the need for this? If we actually need to disable
interrupts, then I'd like to understand why so that we can make sure we
get the ordering right with respect to disabling the device. Also, do we
need to clear the MSI registers too?

I have no justification. Based on the number of drivers that take care
to prevent their HW from generating an interrupt, I thought it would be
required, but I can't find any such requirement explicitly laid out in
the documentation.

When you mention the MSI registers do you mean, for instance,
SMMU_GERROR_IRQ_CFG0? It looks like those are always cleared while
initializing the SMMU so the case where an SMMU transitions from using
MSIs to using wired interrupts between kernels will be handled properly.

My understanding is that kexec will mask irqs at the GIC, so there's not
actually an issue here.

Will

-- 
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.