Re: [PATCH] PCI: revert "Enable PASID only when ACS RR & UF enabled on upstream path"

["Christian König" <christian.koenig@amd.com>]

Am 11.01.23 um 15:20 schrieb Jason Gunthorpe:
> On Wed, Jan 11, 2023 at 03:17:03PM +0100, Christian König wrote:
>> Am 11.01.23 um 15:14 schrieb Jason Gunthorpe:
>>> On Wed, Jan 11, 2023 at 09:54:03PM +0800, Baolu Lu wrote:
>>>> On 2023/1/11 21:44, Jason Gunthorpe wrote:
>>>>>> iommu_enable_pci_caps() in the Intel IOMMU driver. This also does some
>>>>>> handling for ATS, so here we could check the info->ats_supported flag if ACS
>>>>>> needs to be checked or not.
>>>>> *groan*  this is seems wrong 🙁 Lu why are we doing this inside iommu
>>>>> drivers instead of in the device drivers to declare they want to use
>>>>> PASID?
>>>> Currently it's common to enable pasid in the IOMMU drivers, but device
>>>> driver has more knowledge of the device, hence it makes more sense to
>>>> move pci_enable_pasid() to the device driver.
>>> So, lets fix it that way.
>>>
>>> Add the flag to the pci_enable_pasid(), set the flag in the AMD
>>> IOMMU's special AMD GPU only path assuming the device will always use
>>> ATS
>> That will fix at least this the AMD use case.
>>
>>> Do not set the flag in the other iommu drivers
>> Don't we have other hardware which supports ATS as well and might run into
>> the same problem?
> As I said, I think we have only 1 user of the common PASID API and it
> was happy with things as-is, so I think for v6.2 we are fine.
>
> Honestly, not declaring ACS in a 'enterprise' multi-function device is
> already kind of sketchy/rare - even if ATS saves things for the PASID
> case.

Yeah, as I said I've checked a couple of different AMD hardware. And 
what I have available always has ACS, ATS, PRI and PASID enabled together.

That there is a Carizzo variant which enables ATS/PASID but not ACS is 
indeed a bit strange.

Christian.

>
> Jason