On Fri, Aug 25, 2023 at 5:59 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> On Thu, Aug 24, 2023 at 09:37:38AM +0800, Feiyang Chen wrote:
> > When the current state is already PCI_D0, pci_power_up() will return
> > 0 even though dev->pm_cap is not set. In that case, we should not
> > read the PCI_PM_CTRL register in pci_set_full_power_state().
> >
> > There is nothing more needs to be done below in that case.
> > Additionally, pci_power_up() has two callers only and the other one
> > ignores the return value, so we can safely move the current state
> > check from pci_power_up() to pci_set_full_power_state().
>
> Does this fix a bug? I guess it does, because previously
> pci_set_full_power_state() did a config read at 0 + PCI_PM_CTRL, i.e.,
> offset 4, which is actually PCI_COMMAND, and set dev->current_state
> based on that. So dev->current_state is now junk, right?
>
Yes.
> This might account for some "Refused to change power state from %s to D0"
> messages.
>
> How did you find this? It's nice if we can mention a symptom so
> people can connect the problem with this fix.
>
We are attempting to add MSI support for our stmmac driver, but the
pci_alloc_irq_vectors() function always fails.
After looking into it more, we came across the message "Refused to
change power state from D3hot to D0" :)
> This sounds like something that probably should have a stable tag?
>
Do I need to include the symptom and Cc in the commit message and then send v4?
> > Fixes: e200904b275c ("PCI/PM: Split pci_power_up()")
> > Signed-off-by: Feiyang Chen <chenfeiyang@xxxxxxxxxxx>
> > Reviewed-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> > ---
> > drivers/pci/pci.c | 9 +++++----
> > 1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 60230da957e0..7e90ab7b47a1 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -1242,9 +1242,6 @@ int pci_power_up(struct pci_dev *dev)
> > else
> > dev->current_state = state;
> >
> > - if (state == PCI_D0)
> > - return 0;
> > -
> > return -EIO;
> > }
> >
> > @@ -1302,8 +1299,12 @@ static int pci_set_full_power_state(struct pci_dev *dev)
> > int ret;
> >
> > ret = pci_power_up(dev);
> > - if (ret < 0)
> > + if (ret < 0) {
> > + if (dev->current_state == PCI_D0)
> > + return 0;
> > +
> > return ret;
> > + }
> >
> > pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
> > dev->current_state = pmcsr & PCI_PM_CTRL_STATE_MASK;
> > --
> > 2.39.3
> >
