Re: [XEN PATCH v8 1/5] xen/vpci: Clear all vpci status of device

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.05.2024 12:00, Chen, Jiqian wrote:
> On 2024/5/17 17:50, Jan Beulich wrote:
>> On 17.05.2024 11:28, Chen, Jiqian wrote:
>>> On 2024/5/17 16:20, Jan Beulich wrote:
>>>> On 17.05.2024 10:08, Chen, Jiqian wrote:
>>>>> On 2024/5/16 21:08, Jan Beulich wrote:
>>>>>> On 16.05.2024 11:52, Jiqian Chen wrote:
>>>>>>>  struct physdev_pci_device {
>>>>>>>      /* IN */
>>>>>>>      uint16_t seg;
>>>>>>
>>>>>> Is re-using this struct for this new sub-op sufficient? IOW are all
>>>>>> possible resets equal, and hence it doesn't need specifying what kind of
>>>>>> reset was done? For example, other than FLR most reset variants reset all
>>>>>> functions in one go aiui. Imo that would better require only a single
>>>>>> hypercall, just to avoid possible confusion. It also reads as if FLR 
>>>>>> would
>>>>>> not reset as many registers as other reset variants would.
>>>>> If I understood correctly that you mean in this hypercall it needs to 
>>>>> support resetting both one function and all functions of a slot(dev)?
>>>>> But it can be done for caller to use a cycle to call this reset hypercall 
>>>>> for each slot function.
>>>>
>>>> It could, yes, but since (aiui) there needs to be an indication of the
>>>> kind of reset anyway, we can as well avoid relying on the caller doing
>>>> so (and at the same time simplify what the caller needs to do).
>>> Since the corresponding kernel patch has been merged into linux_next branch
>>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20240515&id=b272722511d5e8ae580f01830687b8a6b2717f01,
>>> if it's not very mandatory and necessary, just let the caller handle it 
>>> temporarily.
>>
>> As also mentioned for the other patch having a corresponding kernel one:
>> The kernel patch would imo better not be merged until the new sub-op is
>> actually finalized.
> OK, what should I do next step?
> Upstream a patch to revert the merged patch on kernel side?
> 
>>
>>> Or it can add a new hypercall to reset all functions in one go in future 
>>> potential requirement, like PHYSDEVOP_pci_device_state_reset_all_func.
>>
>> I disagree. We shouldn't introduce incomplete sub-ops. At the very least,
>> if you want to stick to the present form, I'd expect you to supply reasons
>> why distinguishing different reset forms is not necessary (now or later).
> OK, if want to distinguish different reset, is it acceptable to add a 
> parameter, like "u8 flag", and reset every function if corresponding bit is 1?

I'm afraid a boolean won't do, at least not long term. I think it wants to
be an enumeration (i.e. a set of enumeration-like #define-s). And just to
stress it again: The extra argument is _not_ primarily for the looping over
all functions. It is to convey the kind of reset that was done. The single
vs all function(s) aspect is just a useful side effect this will have.

Jan