Re: [PATCH v10 10/10] iommu/arm-smmu-v3: Add stall support for platform devices

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu, 21 Jan 2021 13:36:24 +0100
Jean-Philippe Brucker <jean-philippe@linaro.org> wrote:

> The SMMU provides a Stall model for handling page faults in platform
> devices. It is similar to PCIe PRI, but doesn't require devices to have
> their own translation cache. Instead, faulting transactions are parked
> and the OS is given a chance to fix the page tables and retry the
> transaction.
> 
> Enable stall for devices that support it (opt-in by firmware). When an
> event corresponds to a translation error, call the IOMMU fault handler.
> If the fault is recoverable, it will call us back to terminate or
> continue the stall.
> 
> To use stall device drivers need to enable IOMMU_DEV_FEAT_IOPF, which
> initializes the fault queue for the device.
> 
> Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

One thing inline + one comment which was mostly a case of I ran
out of time to walk through why probe and release aren't symmetric...

> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h   |  43 ++++
>  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c   |  59 +++++-
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   | 185 +++++++++++++++++-
>  3 files changed, 273 insertions(+), 14 deletions(-)
> 

...



> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index db5d6aa76c3a..af6982aca42e 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -32,6 +32,7 @@


...
>  
>  	master->domain = smmu_domain;
> @@ -2484,6 +2624,11 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
>  		master->ssid_bits = min_t(u8, master->ssid_bits,
>  					  CTXDESC_LINEAR_CDMAX);
>  
> +	if ((smmu->features & ARM_SMMU_FEAT_STALLS &&
> +	     device_property_read_bool(dev, "dma-can-stall")) ||
> +	    smmu->features & ARM_SMMU_FEAT_STALL_FORCE)
> +		master->stall_enabled = true;
> +
>  	return &smmu->iommu;
>  
>  err_free_master:
> @@ -2502,6 +2647,7 @@ static void arm_smmu_release_device(struct device *dev)
>  
>  	master = dev_iommu_priv_get(dev);
>  	WARN_ON(arm_smmu_master_sva_enabled(master));
> +	iopf_queue_remove_device(master->smmu->evtq.iopf, dev);
>  	arm_smmu_detach_dev(master);
>  	arm_smmu_disable_pasid(master);
>  	arm_smmu_remove_master(master);

The lack of symmetry here bothers me a bit, but it's already true, so I guess
this case is fine as well.

...
>  
> @@ -2785,6 +2946,7 @@ static int arm_smmu_cmdq_init(struct arm_smmu_device *smmu)
>  static int arm_smmu_init_queues(struct arm_smmu_device *smmu)
>  {
>  	int ret;
> +	bool sva = smmu->features & ARM_SMMU_FEAT_STALLS;

FEAT_SVA?

>  
>  	/* cmdq */
>  	ret = arm_smmu_init_one_queue(smmu, &smmu->cmdq.q, ARM_SMMU_CMDQ_PROD,
> @@ -2804,6 +2966,12 @@ static int arm_smmu_init_queues(struct arm_smmu_device *smmu)
>  	if (ret)
>  		return ret;
>  
> +	if (sva && smmu->features & ARM_SMMU_FEAT_STALLS) {

Isn't this checking same thing twice?

> +		smmu->evtq.iopf = iopf_queue_alloc(dev_name(smmu->dev));
> +		if (!smmu->evtq.iopf)
> +			return -ENOMEM;
> +	}
> +
>  	/* priq */
>  	if (!(smmu->features & ARM_SMMU_FEAT_PRI))
>  		return 0;
> @@ -3718,6 +3886,7 @@ static int arm_smmu_device_remove(struct platform_device *pdev)
>  	iommu_device_unregister(&smmu->iommu);
>  	iommu_device_sysfs_remove(&smmu->iommu);
>  	arm_smmu_device_disable(smmu);
> +	iopf_queue_free(smmu->evtq.iopf);
>  
>  	return 0;
>  }