linux-kernel - Re: [PATCH 02/13] iommu: Move bus setup to IOMMU device registration

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Message-ID: <1d9a2146-9e48-ba97-d049-5d2332ebbd3a@arm.com>
Date:   Mon, 18 Apr 2022 23:09:36 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>, joro@...tes.org,
        will@...nel.org
Cc:     iommu@...ts.linux-foundation.org, sven@...npeter.dev,
        robdclark@...il.com, m.szyprowski@...sung.com,
        yong.wu@...iatek.com, mjrosato@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, zhang.lyra@...il.com,
        thierry.reding@...il.com, vdumpa@...dia.com,
        jean-philippe@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/13] iommu: Move bus setup to IOMMU device registration

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.