Re: [PATCH 1/4] PCI/pwrctrl: Move creation of pwrctrl devices to pci_scan_device()

[Lukas Wunner <lukas@wunner.de>]

On Mon, Dec 16, 2024 at 10:45:21AM +0530, Manivannan Sadhasivam wrote:
> On Sun, Dec 15, 2024 at 06:19:22PM +0100, Lukas Wunner wrote:
> > On Tue, Dec 10, 2024 at 03:25:24PM +0530, Manivannan Sadhasivam wrote:
> > > diff --git a/drivers/pci/pwrctrl/core.c b/drivers/pci/pwrctrl/core.c
> > > index 2fb174db91e5..9cc7e2b7f2b5 100644
> > > --- a/drivers/pci/pwrctrl/core.c
> > > +++ b/drivers/pci/pwrctrl/core.c
> > > @@ -44,7 +44,7 @@ static void rescan_work_func(struct work_struct *work)
> > >  						   struct pci_pwrctrl, work);
> > >  
> > >  	pci_lock_rescan_remove();
> > > -	pci_rescan_bus(to_pci_dev(pwrctrl->dev->parent)->bus);
> > > +	pci_rescan_bus(to_pci_host_bridge(pwrctrl->dev->parent)->bus);
> > >  	pci_unlock_rescan_remove();
> > >  }
> > 
> > Remind me, what's the purpose of this?  I'm guessing that it
> > recursively creates the platform devices below the newly
> > powered up device, is that correct?  If so, is it still
> > necessary?  Doesn't the new approach automatically create
> > those devices upon their enumeration?
> 
> If the pwrctrl driver is available at the time of platform device creation,
> this is not needed. But if the driver is not available at that time and
> probed later, then we need to rescan the bus to enumerate the devices.

I see.  Sounds like this can be made conditional on the caller
being a module.  I think you could achieve this with the following
in pci_pwrctl_device_set_ready():

-	schedule_work(&pwrctl->work);
+	if (is_module_address(_RET_IP_))
+		schedule_work(&pwrctl->work);

Though you'd also have to declare pci_pwrctl_device_set_ready()
"__attribute__((always_inline))" so that it gets inlined into
devm_pci_pwrctl_device_set_ready() and the condition works there
as well.

I'm wondering whether the bus notifier is still necessary with
the new scheme.  Since the power control device is instantiated
and destroyed in unison with the pci_dev, can't the device link
always be created on instantiation of the power control device?

Thanks,

Lukas