On 2023/8/15 1:25, Jason Gunthorpe wrote:

Ah, I went over all this again and decided to try again, it is too
complicated. This patch can do what the commit message says and the
following patches are even simpler:

Yes. This method is more concise. Some nits below.

/*
  * Combine the driver's choosen def_domain_type across all the devices in a
  * group. Drivers must give a consistent result.
  */
static int iommu_get_def_domain_type(struct iommu_group *group,
				     struct device *dev, int cur_type)
{
	const struct iommu_ops *ops = group_iommu_ops(group);
	int type;

	if (!ops->def_domain_type)
		return cur_type;

	type = ops->def_domain_type(dev);
	if (!type || cur_type == type)
		return cur_type;
	if (!cur_type)
		return type;

	dev_err_ratelimited(
		dev,
		"IOMMU driver error, requesting conflicting def_domain_type, %s and %s, for devices in group %u.\n",
		iommu_domain_type_str(cur_type), iommu_domain_type_str(type),
		group->id);

	/*
	 * Try to recover, drivers are allowed to force IDENITY or DMA, IDENTITY
	 * takes precedence.
	 */
	if (cur_type || type == IOMMU_DOMAIN_IDENTITY)
		return IOMMU_DOMAIN_IDENTITY;

No need to check cur_type. It already returned if cur_type is 0.

	return cur_type;
}

/*
  * A target_type of 0 will select the best domain type. 0 can be returned in
  * this case meaning the global default should be used.
  */
static int iommu_get_default_domain_type(struct iommu_group *group,
					 int target_type)
{
	struct device *untrusted = NULL;
	struct group_device *gdev;
	int driver_type = 0;

	lockdep_assert_held(&group->mutex);

	/*
	 * ARM32 drivers supporting CONFIG_ARM_DMA_USE_IOMMU can declare an
	 * identity_domain and it will automatically become their default
	 * domain. Later on ARM_DMA_USE_IOMMU will install its UNMANAGED domain.
	 * Override the selection to IDENTITY.
	 */
	if (IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)) {
		static_assert(!(IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU) &&
				IS_ENABLED(CONFIG_IOMMU_DMA)));

IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU) is duplicate with the condition in 
the if statement. So only
		static_assert(!IS_ENABLED(CONFIG_IOMMU_DMA));
?

		driver_type = IOMMU_DOMAIN_IDENTITY;
	}

	for_each_group_device(group, gdev) {
		driver_type = iommu_get_def_domain_type(group, gdev->dev,
							driver_type);

No need to call this in the loop body?

		if (dev_is_pci(gdev->dev) && to_pci_dev(gdev->dev)->untrusted) {
			/*
			 * No ARM32 using systems will set untrusted, it cannot
			 * work.
			 */
			if (WARN_ON(IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)))
				return -1;
			untrusted = gdev->dev;
		}
	}

	if (untrusted) {
		if (driver_type && driver_type != IOMMU_DOMAIN_DMA) {
			dev_err_ratelimited(
				untrusted,
				"Device is not trusted, but driver is overriding group %u to %s, refusing to probe.\n",
				group->id, iommu_domain_type_str(driver_type));
			return -1;
		}
		driver_type = IOMMU_DOMAIN_DMA;
	}

	if (target_type) {
		if (driver_type && target_type != driver_type)
			return -1;
		return target_type;
	}
	return driver_type;
}

Best regards,
baolu

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