Re: [RFC PATCH] xen/amd-iommu: Add interrupt remapping quirk for ath11k

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.02.2025 17:49, Jason Andryuk wrote:
> On 2025-02-27 03:54, Jan Beulich wrote:
>> On 26.02.2025 22:11, Jason Andryuk wrote:
>>> Signed-off-by: Xenia Ragiadakou <xenia.ragiadakou@xxxxxxx>
>>> Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
>>
>> Just to clarify: Who's the original patch author? The common expectation
>> is that the first S-o-b: matches From:.
> 
> I took Xenia's changes to xen/drivers/passthrough/pci.c and 
> xen/include/xen/pci.h from an earlier patch and re-used them.  I wrote 
> the rest, so I put myself in the Form: line.

Unusual arrangements of tags typically call for some clarification in ...

>>> ---

... the post-commit-message area. In the case here the question arises
whether a different tag (Co-Developed-by:?) might not be better.

>>> --- a/xen/drivers/passthrough/amd/iommu_intr.c
>>> +++ b/xen/drivers/passthrough/amd/iommu_intr.c
>>> @@ -543,6 +543,31 @@ int cf_check amd_iommu_msi_msg_update_ire(
>>>       if ( !msg )
>>>           return 0;
>>>   
>>> +    if ( pdev->gvec_as_irte_idx && amd_iommu_perdev_intremap )
>>> +    {
>>> +        int new_remap_index = 0;
>>> +        if ( msi_desc->gvec )
>>> +        {
>>> +            printk("%pp: gvec remap_index %#x -> %#x\n", &pdev->sbdf,
>>> +                   msi_desc->remap_index, msi_desc->gvec);
>>> +            new_remap_index = msi_desc->gvec;
>>> +        }
>>> +
>>> +        if ( new_remap_index && new_remap_index != msi_desc->remap_index &&
>>> +             msi_desc->remap_index != -1 )
>>> +        {
>>> +            /* Clear any existing entries */
>>> +            update_intremap_entry_from_msi_msg(iommu, bdf, nr,
>>> +                                               &msi_desc->remap_index,
>>> +                                               NULL, NULL);
>>> +
>>> +            for ( i = 0; i < nr; ++i )
>>> +                msi_desc[i].remap_index = -1;
>>> +
>>> +            msi_desc->remap_index = new_remap_index;
>>
>> You zap nr entries, and then set only 1? Doesn't the zapping loop need to
>> instead be a setting one? Perhaps with a check up front that the last value
>> used will still fit in 8 bits? Or else make applying the quirk conditional
>> upon nr == 1?
> 
> The code below here sets all `nr` entries on success:
> 
>      rc = update_intremap_entry_from_msi_msg(iommu, bdf, nr,
>                                              &msi_desc->remap_index,
>                                              msg, &data);
>      if ( !rc )
>      {
>          for ( i = 1; i < nr; ++i )
>              msi_desc[i].remap_index = msi_desc->remap_index + i;
>          msg->data = data;
>      }
> 
>      return rc;

Ah, yes, I see now how this matches other behavior in the function.

> Maybe all the remap_index settting should be moved into 
> update_intremap_entry_from_msi_msg()?

That would require passing in msi_desc (or making assumptions on the
passed in "int *remap_index"), neither of which looks very attractive
to me.

Jan