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Message-ID: <1d9a2146-9e48-ba97-d049-5d2332ebbd3a@arm.com>
Date:   Mon, 18 Apr 2022 23:09:36 +0100
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Subject: Re: [PATCH 02/13] iommu: Move bus setup to IOMMU device registration
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To:     Lu Baolu <baolu.lu@linux.intel.com>, joro@8bytes.org,
        will@kernel.org
Cc:     iommu@lists.linux-foundation.org, sven@svenpeter.dev,
        robdclark@gmail.com, m.szyprowski@samsung.com,
        yong.wu@mediatek.com, mjrosato@linux.ibm.com,
        gerald.schaefer@linux.ibm.com, zhang.lyra@gmail.com,
        thierry.reding@gmail.com, vdumpa@nvidia.com,
        jean-philippe@linaro.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
References: <cover.1649935679.git.robin.murphy@arm.com>
 <e607a32be8e84c56d65160902f4bd3fb434ee9d3.1649935679.git.robin.murphy@arm.com>
 <d838c7f8-2d31-2327-9b4d-c05b06a516bb@linux.intel.com>
From:   Robin Murphy <robin.murphy@arm.com>
In-Reply-To: <d838c7f8-2d31-2327-9b4d-c05b06a516bb@linux.intel.com>
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On 2022-04-16 01:04, Lu Baolu wrote:
> On 2022/4/14 20:42, Robin Murphy wrote:
>> @@ -1883,27 +1900,12 @@ static int iommu_bus_init(struct bus_type *bus)
>>    */
>>   int bus_set_iommu(struct bus_type *bus, const struct iommu_ops *ops)
>>   {
>> -    int err;
>> -
>> -    if (ops == NULL) {
>> -        bus->iommu_ops = NULL;
>> -        return 0;
>> -    }
>> -
>> -    if (bus->iommu_ops != NULL)
>> +    if (bus->iommu_ops && ops && bus->iommu_ops != ops)
>>           return -EBUSY;
>>       bus->iommu_ops = ops;
> 
> Do we still need to keep above lines in bus_set_iommu()?

It preserves the existing behaviour until each callsite and its 
associated error handling are removed later on, which seems like as good 
a thing to do as any. Since I'm already relaxing iommu_device_register() 
to a warn-but-continue behaviour while it keeps the bus ops on 
life-support internally, I figured not changing too much at once would 
make it easier to bisect any potential issues arising from this first step.

Thanks,
Robin.