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

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Date:   Sat, 23 Apr 2022 16:01:59 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....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

Hi Robin,

On 2022/4/19 15:20, Robin Murphy wrote:
> On 2022-04-19 00:37, Lu Baolu wrote:
>> 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.
> 
> I haven't bothered with separate branches since there's so many 
> different pieces in-flight, but my complete (unstable) development 
> branch can be found here:
> 
> https://gitlab.arm.com/linux-arm/linux-rm/-/commits/iommu/bus
> 
> For now I'd recommend winding the head back to "iommu: Clean up 
> bus_set_iommu()" for testing - some of the patches above that have 
> already been posted and picked up by their respective subsystems, but 
> others are incomplete and barely compile-tested. I'll probably rearrange 
> it later this week to better reflect what's happened so far.

I wound the head back to "iommu: Clean up bus_set_iommu" and tested it
on an Intel machine. It got stuck during boot. This test was on a remote
machine and I have no means to access it physically. So I can't get any
kernel debugging messages. (I have to work from home these days. :-()

I guess it's due to the fact that intel_iommu_probe_device() callback
only works for the pci devices. The issue occurs when probing a device
other than a PCI one.

Best regards,
baolu