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

[Bjorn Helgaas <helgaas@kernel.org>]

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>
---
 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