Re: [PATCH v3 2/2] PCI: pciehp: Clear the optional capabilities in DEVCTL2 on a hot-plug

[Felix Kuehling]

On 2023-06-22 23:42, Lukas Wunner wrote:
> [cc += Jay, Felix]
>
> On Thu, Jun 22, 2023 at 02:02:12PM -0700, Smita Koralahalli wrote:
> > Would it be fair to just reuse pci_enable_atomic_ops_to_root() for
> > Atomic_Ops configuration?
> Hm, that's a good question.  I'm not an expert on that corner of
> the PCI core.
>
> But indeed what you could try is amend that function to not only
> *set* PCI_EXP_DEVCTL2_ATOMIC_REQ if it's supported, but to also
> *clear* it if it's not supported.
>
> And you'd have to call pci_enable_atomic_ops_to_root() on enumeration,
> e.g. from pci_init_capabilities().
>
> That should obviate the need to call pci_enable_atomic_ops_to_root()
> from drivers, so you could probably remove the call from all the
> drivers which currently call it (amdgpu, infiniband, mellanox),
> in one separate patch per driver.
>
> An then you could drop the EXPORT clause for pci_enable_atomic_ops_to_root()
> and make it private to the PCI core.
Then our driver would need an alternative way to determine whether 
atomic capabilities are enabled for a device. We currently use the 
return value from pci_enable_atomic_ops_to_root to determine this.

Regards,
  Felix


> So that would be 5 patches (enablement/disablement on enumeration,
> amendmend of the 3 drivers, making the call private).
>
> I'm not sure if anyone will cry foul if you do that but if you want
> to give it a try, go for it. :)
>
> I don't now why commit 430a23689dea, which introduced
> pci_enable_atomic_ops_to_root(), chose to add it as a library function
> which is only called from specific drivers, instead of universally
> enabling the feature for all devices.  Adding the commit authors to cc
> so they can chime in.
>
> Thanks,
>
> Lukas