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

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Date:   Tue, 19 Apr 2022 07:37:57 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>, joro@...tes.org,
        will@...nel.org
Cc:     baolu.lu@...ux.intel.com, 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 2022/4/19 6:09, Robin Murphy wrote:
> 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.

Fair enough. Thank you for the explanation.

Do you have a public tree that I could pull these patches and try them
on an Intel hardware? Or perhaps you have done this? I like the whole
idea of this series, but it's better to try it with a real hardware.

Best regards,
baolu