Re: [PATCH v2] PCI/PM: Only read PCI_PM_CTRL register when available

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Tue, 22 Aug 2023, Anders Roxell wrote:

> On Tue, 22 Aug 2023 at 13:55, Feiyang Chen <chenfeiyang@loongson.cn> 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().
> >
> > Fixes: e200904b275c ("PCI/PM: Split pci_power_up()")
> > Signed-off-by: Feiyang Chen <chenfeiyang@loongson.cn>
> > ---
> >  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;
> 
> In fuction pci_power_up() there's another if-statement
> if (state == PCI_D0)
>         goto end;
>
> That also will return 0 if need_restore isn't true.
> What will happen then?

That case is only after pci_power_up() has returned because of 
!dev->pm_cap. As such, it looks unrelated to the case this patch is fixing 
which is the read from PCI_PM_CTRL when dev->pm_cap is not there.

> Would this work?
> 
>         ret = pci_power_up(dev);
> -       if (ret < 0)
> +       if (ret <= 0)
>                  return ret;


-- 
 i.