linux-kernel - Re: [PATCH 2/5] PCI / PM: Return error when changing power state from D3cold

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Message-ID: <CAJZ5v0gN+r+6UiUFGWmqzudGDqn=oWg0sRg-8jjX2HMJwLdxAg@mail.gmail.com>
Date:   Mon, 5 Aug 2019 23:15:13 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Linux PCI <linux-pci@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Keith Busch <keith.busch@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 2/5] PCI / PM: Return error when changing power state from D3cold

On Mon, Aug 5, 2019 at 10:52 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> From: Bjorn Helgaas <bhelgaas@...gle.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@...gle.com>

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

> ---
>  drivers/pci/pci.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index bfc739dc6ada..984171d40858 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -851,6 +851,11 @@ 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, "device not responding; can't change to power state D%d\n",
> +                       state);
> +               return -EIO;
> +       }
>
>         /*
>          * If we're (effectively) in D3, force entire word to 0.
> --
> 2.22.0.770.g0f2c4a37fd-goog
>