Re: [PATCH v2] PCI/PM: Restore BARs after powering up during enumeration

[Rafael J. Wysocki (Intel)]

On Tue, Oct 13, 2026 at 5:52 PM Rafael J. Wysocki (Intel)
<rafael@xxxxxxxxxx> wrote:
>
> On Tue, Oct 13, 2026 at 5:41 PM Mario Limonciello
> <mario.limonciello@xxxxxxx> wrote:
> >
> >
> >
> > On 10/13/26 10:23, Rafael J. Wysocki (Intel) wrote:
> > > On Tue, Oct 13, 2026 at 8:10 AM Keng-Yu Lin <keng-yu.lin@xxxxxxx> wrote:
> > >>
> > >> Hi Rafael, Mario,
> > >>
> > >> The initial read is not needed to fix the reported D3hot-to-D0
> > >> failure. I added it to avoid extra BAR writes on devices already
> > >> in D0.
> > >>
> > >> pci_power_up() does update current_state, but need_restore is
> > >> calculated before that update. The check includes:
> > >>
> > >>          dev->current_state >= PCI_D3hot
> > >>
> > >> For an initially unknown device with PMCSR reporting D0 and
> > >> No_Soft_Reset clear, this still requests a BAR restore. Reading
> > >> the state first avoids that request, although the final
> > >> current_state is D0 either way.
> > >
> > > Fair enough, but if the device is in D0 already, it need not be
> > > powered up, so if you make a point to update the power state upfront,
> > > you may as well skip the power up if the outcome is D0.
> >
> > It actually does need to have all the ACPI calls that happen as part of
> > the D0 transition though like _REG.
>
> Good point.
>
> This basically means that the upfront power state check belongs to the
> logic to determine whether or not to restore the BARs which should be
> part of pci_power_up().
>
> So now the question is, if this upfront power state check is done, is
> it still useful to read PMCSR after calling
> platform_pci_set_power_state() in pci_power_up()?

Or what about using the following sequence:

pci_update_current_state(dev, PCI_UNKNOWN);
if (dev->current_state == PCI_D0) {
        /* No need to do a full power-up, just sync-up the platform state. */
        platform_pci_set_power_state(dev, PCI_D0);
} else {
        /* Power up the device and restore BARs if necessary. */
        pci_set_full_power_state(dev, false);
}
pci_update_current_state(dev, PCI_D0);