Re: [PATCH v3 06/20] iommu/mtk: Remove detach_dev callback

Robin Murphy
2022-11-29T11:45:59Z

On 2022-11-29 02:07, Baolu Lu wrote:
> On 11/28/22 9:59 PM, Robin Murphy wrote:
>> On 2022-11-28 13:49, Jason Gunthorpe wrote:
>>> On Mon, Nov 28, 2022 at 02:46:34PM +0800, Lu Baolu wrote:
>>>> The IOMMU driver supports default domain, so the detach_dev op will
>>>> never
>>>> be called. Remove it to avoid dead code.
>>>>
>>>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>>>> ---
>>>>   drivers/iommu/mtk_iommu.c | 9 ---------
>>>>   1 file changed, 9 deletions(-)
>>>
>>> I listed this driver as not supporting default domains:
>>>
>>> https://lore.kernel.org/linux-iommu/20220516135741.GV1343366@nvidia.com/
>>>
>>> ?
>>>
>>> Has something changed? Did I get it wrong?
>>
>> static struct iommu_domain *mtk_iommu_domain_alloc(unsigned type)
>> {
>>      struct mtk_iommu_domain *dom;
>>
>>      if (type != IOMMU_DOMAIN_DMA && type != IOMMU_DOMAIN_UNMANAGED)
>>          return NULL;
>> ...
>>
>>
>> This one runs on arm64, so has always supported default domains for
>> iommu-dma to work.
>
> This, together with several other ones, only support IOMMU_DOMAIN_DMA
> type of default domain. The iommu core handle this by falling back to
> IOMMU_DOMAIN_DMA if other types fail.
>
>         dom = __iommu_domain_alloc(bus, type);
>         if (!dom && type != IOMMU_DOMAIN_DMA) {
>                 dom = __iommu_domain_alloc(bus, IOMMU_DOMAIN_DMA);
>                 if (dom)
>                         pr_warn("Failed to allocate default IOMMU
> domain of type %u for group %s - Falling back to IOMMU_DOMAIN_DMA",
>                                 type, group->name);
>         }
>
> I have another cleanup series:
>
> https://github.com/LuBaolu/intel-iommu/commits/iommu-use-def_default_type-wip
>
> which adds IOMMU_DOMAIN_DMA default domain type requirement in the
> def_domain_type callback. I planed to bring that to discussion after
> this one.

Per the discussion over on the s390 thread, I think that would be a step
in the wrong direction. I'd prefer to keep .def_domain_type for
device-specific requirements and express general driver domain support a
different way. If the IOMMU_DOMAIN_DMA fallback is worth removing then
the one for IOMMU_DOMAIN_BLOCKED is as well - no point doing half the job ;)

Thanks,
Robin.