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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

> 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).

Jan