Subject: [PATCH v2 6/9] iommu/arm-smmu: to support probe deferral

From: [email-masked] (Robin Murphy)
Date: Wed, 08 Jul 2015 14:13:20 +0100

On 07/07/15 04:30, Zhen Lei wrote:
> For pci devices, only the root nodes have "iommus" property. So we
> should traverse all of its sub nodes in of_xlate.

I don't really follow this description; only the host controller is 
described in DT - the devices behind it are probed dynamically and don't 
have nodes to traverse.

> Signed-off-by: Zhen Lei <[email-masked]>
> ---
>   drivers/iommu/arm-smmu-v3.c | 119 +++++++++++++++++++++++++++++++++-----------
>   1 file changed, 89 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index d6e3494..c569539 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -30,6 +30,8 @@
>   #include <linux/of_address.h>
>   #include <linux/pci.h>
>   #include <linux/platform_device.h>
> +#include <linux/of_iommu.h>
> +#include <linux/of_platform.h>
>
>   #include "io-pgtable.h"
>
> @@ -1741,10 +1743,23 @@ static void __arm_smmu_release_pci_iommudata(void *data)
>   	kfree(data);
>   }
>
> -static struct arm_smmu_device *arm_smmu_get_for_pci_dev(struct pci_dev *pdev)
> +static struct arm_smmu_device *find_smmu_by_node(struct device_node *np)
> +{
> +	struct platform_device *pdev;
> +
> +	/* to ensure np is a smmu device node */
> +	if (!of_iommu_get_ops(np))
> +		return NULL;
> +
> +	pdev = of_find_device_by_node(np);
> +	if (!pdev)
> +		return NULL;
> +
> +	return platform_get_drvdata(pdev);
> +}
> +
> +static struct device_node *arm_smmu_get_pci_dev_root(struct pci_dev *pdev)
>   {
> -	struct device_node *of_node;
> -	struct arm_smmu_device *curr, *smmu = NULL;
>   	struct pci_bus *bus = pdev->bus;
>
>   	/* Walk up to the root bus */
> @@ -1752,21 +1767,7 @@ static struct arm_smmu_device *arm_smmu_get_for_pci_dev(struct pci_dev *pdev)
>   		bus = bus->parent;
>
>   	/* Follow the "iommus" phandle from the host controller */

Either update comments to reflect what the new code does, or remove them 
along with the code they describe.

> -	of_node = of_parse_phandle(bus->bridge->parent->of_node, "iommus", 0);
> -	if (!of_node)
> -		return NULL;
> -
> -	/* See if we can find an SMMU corresponding to the phandle */
> -	spin_lock(&arm_smmu_devices_lock);
> -	list_for_each_entry(curr, &arm_smmu_devices, list) {
> -		if (curr->dev->of_node == of_node) {
> -			smmu = curr;
> -			break;
> -		}
> -	}
> -	spin_unlock(&arm_smmu_devices_lock);
> -	of_node_put(of_node);
> -	return smmu;
> +	return bus->bridge->parent->of_node;
>   }
>
>   static bool arm_smmu_sid_in_range(struct arm_smmu_device *smmu, u32 sid)
> @@ -1779,27 +1780,21 @@ static bool arm_smmu_sid_in_range(struct arm_smmu_device *smmu, u32 sid)
>   	return sid < limit;
>   }
>
> -static int arm_smmu_add_device(struct device *dev)
> +static int arm_smmu_add_device(struct device *dev, u32 sid)
>   {
>   	int i, ret;
> -	u32 sid, *sids;
> -	struct pci_dev *pdev;
> +	u32 *sids;
>   	struct iommu_group *group;
>   	struct arm_smmu_group *smmu_group;
>   	struct arm_smmu_device *smmu;
>
> -	/* We only support PCI, for now */
> -	if (!dev_is_pci(dev))
> -		return -ENODEV;
> -
> -	pdev = to_pci_dev(dev);
>   	group = iommu_group_get_for_dev(dev);
>   	if (IS_ERR(group))
>   		return PTR_ERR(group);
>
>   	smmu_group = iommu_group_get_iommudata(group);
>   	if (!smmu_group) {
> -		smmu = arm_smmu_get_for_pci_dev(pdev);
> +		smmu = dev->archdata.iommu;
>   		if (!smmu) {
>   			ret = -ENOENT;
>   			goto out_put_group;
> @@ -1819,8 +1814,6 @@ static int arm_smmu_add_device(struct device *dev)
>   		smmu = smmu_group->smmu;
>   	}
>
> -	/* Assume SID == RID until firmware tells us otherwise */
> -	pci_for_each_dma_alias(pdev, __arm_smmu_get_pci_sid, &sid);
>   	for (i = 0; i < smmu_group->num_sids; ++i) {
>   		/* If we already know about this SID, then we're done */
>   		if (smmu_group->sids[i] == sid)
> @@ -1862,6 +1855,7 @@ out_put_group:
>
>   static void arm_smmu_remove_device(struct device *dev)
>   {
> +	dev->archdata.iommu = NULL;
>   	iommu_group_remove_device(dev);
>   }
>
> @@ -1909,7 +1903,68 @@ out_unlock:
>   	return ret;
>   }
>
> +static int arm_smmu_of_xlate(struct device *dev, struct of_phandle_args *args)
> +{
> +	int ret;
> +	struct arm_smmu_device *smmu;
> +
> +	/*
> +	 * We can sure that args->np is a smmu device node, because this
> +	 * function was called by of_xlate hook.
> +	 *
> +	 * And in arm_smmu_device_dt_probe:
> +	 *	platform_set_drvdata(pdev, smmu);
> +	 *	of_iommu_set_ops(smmu->dev->of_node, &arm_smmu_ops);
> +	 *
> +	 * It seems impossible return NULL in normal times.
> +	 */
> +	smmu = find_smmu_by_node(args->np);
> +	if (!smmu) {
> +		dev_err(dev, "unknown error caused smmu driver crashed\n");
> +		return -ENODEV;
> +	}
> +
> +	if (!dev->archdata.iommu)
> +		dev->archdata.iommu = smmu;
> +
> +	if (dev->archdata.iommu != smmu) {
> +		dev_err(dev, "behinds more than one smmu\n");
> +		return -EINVAL;
> +	}
> +
> +	/* We only support PCI, for now */
> +	if (!dev_is_pci(dev)) {
> +		return -ENODEV;
> +	} else {
> +		u32 sid;
> +		struct device_node *of_root;
> +		struct pci_dev *pdev = NULL;
> +
> +		for_each_pci_dev(pdev) {

Given that we get here before the host controller's driver probe, is 
this really going to work? Either way, it looks very dodgy.

> +			of_root = arm_smmu_get_pci_dev_root(pdev);
> +			if (of_root != dev->of_node)
> +				continue;
> +
> +			/*
> +			 * Assume SID == RID until firmware tells us otherwise
> +			 */
> +			pci_for_each_dma_alias(pdev,
> +					__arm_smmu_get_pci_sid, &sid);
> +
> +			pdev->dev.archdata.iommu = smmu;
> +			ret = arm_smmu_add_device(dev, sid);
> +			if (ret) {
> +				dev_err(dev, "failed to add into SMMU\n");
> +				return ret;
> +			}
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>   static struct iommu_ops arm_smmu_ops = {
> +	.of_xlate		= arm_smmu_of_xlate,
>   	.capable		= arm_smmu_capable,
>   	.domain_alloc		= arm_smmu_domain_alloc,
>   	.domain_free		= arm_smmu_domain_free,
> @@ -1918,7 +1973,6 @@ static struct iommu_ops arm_smmu_ops = {
>   	.map			= arm_smmu_map,
>   	.unmap			= arm_smmu_unmap,
>   	.iova_to_phys		= arm_smmu_iova_to_phys,
> -	.add_device		= arm_smmu_add_device,

It might not be an immediate concern, but I think subverting the normal 
add_device process this way also completely breaks any kind of device 
hotplug.

>   	.remove_device		= arm_smmu_remove_device,
>   	.domain_get_attr	= arm_smmu_domain_get_attr,
>   	.domain_set_attr	= arm_smmu_domain_set_attr,
> @@ -2626,6 +2680,9 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
>   	spin_lock(&arm_smmu_devices_lock);
>   	list_add(&smmu->list, &arm_smmu_devices);
>   	spin_unlock(&arm_smmu_devices_lock);
> +	platform_set_drvdata(pdev, smmu);
> +	of_iommu_set_ops(smmu->dev->of_node, &arm_smmu_ops);
> +
>   	return 0;
>
>   out_free_structures:
> @@ -2697,6 +2754,8 @@ static void __exit arm_smmu_exit(void)
>   subsys_initcall(arm_smmu_init);
>   module_exit(arm_smmu_exit);
>
> +IOMMU_OF_DECLARE(arm_smmu_v3, "arm,smmu-v3", NULL);
> +
>   MODULE_DESCRIPTION("IOMMU API for ARM architected SMMUv3 implementations");
>   MODULE_AUTHOR("Will Deacon <[email-masked]>");
>   MODULE_LICENSE("GPL v2");
> --
> 1.8.0
>
>
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