Re: [PATCH 3/3] PCI / PM: Return error when changing power state from D3cold

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, Aug 22, 2019 at 10:06 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> From: Bjorn Helgaas <bhelgaas@google.com>
>
> pci_raw_set_power_state() uses the Power Management capability to change a
> device's power state.  The capability is in config space, which is
> accessible in D0, D1, D2, and D3hot, but not in D3cold.
>
> If we call pci_raw_set_power_state() on a device that's in D3cold, config
> reads fail and return ~0 data, which we erroneously interpreted as "the
> device is in D3hot", leading to messages like this:
>
>   pcieport 0000:03:00.0: Refused to change power state, currently in D3
>
> The PCI_PM_CTRL has several RsvdP fields, so ~0 is never a valid register
> value.  Notice if we get that data, print a more informative message, and
> return an error.
>
> Changing the power state of a device from D3cold must be done by a platform
> power management method or some other non-config space mechanism.
>
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
>  drivers/pci/pci.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 5f0a3145c3f2..41112af189a8 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -853,6 +853,12 @@ static int pci_raw_set_power_state(struct pci_dev *dev, pci_power_t state)
>                 return -EIO;
>
>         pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
> +       if (pmcsr == (u16) PCI_ERROR_RESPONSE) {
> +               pci_err(dev, "can't access config space to change power state from %s to %s\n",
> +                       pci_power_name(dev->current_state),
> +                       pci_power_name(state));
> +               return -EIO;
> +       }
>
>         /*
>          * If we're (effectively) in D3, force entire word to 0.
> @@ -893,8 +899,9 @@ static int pci_raw_set_power_state(struct pci_dev *dev, pci_power_t state)
>         pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
>         dev->current_state = (pmcsr & PCI_PM_CTRL_STATE_MASK);
>         if (dev->current_state != state && printk_ratelimit())
> -               pci_info(dev, "refused to change power state (currently %s)\n",
> -                        pci_power_name(dev->current_state));
> +               pci_info(dev, "refused to change power state from %s to %s\n",
> +                        pci_power_name(dev->current_state),
> +                        pci_power_name(state));
>
>         /*
>          * According to section 5.4.1 of the "PCI BUS POWER MANAGEMENT
> --
> 2.23.0.187.g17f5b7556c-goog
>