linux-kernel - Re: [PATCH v3 04/15] iommu: Move bus setup to IOMMU device registration

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Date:   Wed, 6 Jul 2022 10:35:22 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>, joro@...tes.org
Cc:     baolu.lu@...ux.intel.com, will@...nel.org, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org,
        suravee.suthikulpanit@....com, vasant.hegde@....com,
        mjrosato@...ux.ibm.com, gerald.schaefer@...ux.ibm.com,
        schnelle@...ux.ibm.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 04/15] iommu: Move bus setup to IOMMU device
 registration

On 2022/7/6 01:08, Robin Murphy wrote:
> @@ -202,12 +210,32 @@ int iommu_device_register(struct iommu_device *iommu,
>   	spin_lock(&iommu_device_lock);
>   	list_add_tail(&iommu->list, &iommu_device_list);
>   	spin_unlock(&iommu_device_lock);
> +
> +	for (int i = 0; i < ARRAY_SIZE(iommu_buses); i++) {
> +		struct bus_type *bus = iommu_buses[i];
> +		int err;
> +
> +		if (bus->iommu_ops && bus->iommu_ops != ops) {
> +			err = -EBUSY;
> +		} else {
> +			bus->iommu_ops = ops;
> +			err = bus_iommu_probe(bus);
> +		}
> +		if (err) {
> +			iommu_device_unregister(iommu);
> +			return err;
> +		}
> +	}
> +
>   	return 0;
>   }
>   EXPORT_SYMBOL_GPL(iommu_device_register);

With bus_set_iommu() retired, my understanding is that now we embrace
the first-come-first-serve policy for bus->iommu_ops setting. This will
lead to problem in different iommu_ops for different bus case. Did I
overlook anything?

Best regards,
baolu