[PATCH v2 2/2] PCI: Wait for device readiness after D3hot -> D0uninitialized transition

[Bjorn Helgaas <helgaas@kernel.org>]

From: Bjorn Helgaas <helgaas@kernel.org>

For a device that advertises No_Soft_Reset == 0, a transition from D3hot to
D0uninitialized is a soft reset, and the resulting internal device state is
undefined.

Per PCIe r7.0, sec 2.3.1, a transition from D3hot to D0uninitialized
mandates a minimum 10 ms delay before accessing the device. Following this
delay, the device is permitted to respond to initial configuration requests
with a Request Retry Status (RRS) completion status if it needs more time
to initialize.

Call pci_dev_wait() after pci_power_up() performs a D3hot->D0uninitialized
transition to ensure the device is ready to accept config accesses, as is
done after the similar transition in pci_pm_reset().

If the device is already ready, this is essentially a no-op except for one
additional config read.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/pci.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 5a9af0bb2c71..8228d2782f95 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1300,7 +1300,18 @@ int pci_power_up(struct pci_dev *dev)
 	bool need_restore;
 	pci_power_t state;
 	u16 pmcsr;
+	int ret;
 
+	/*
+	 * When setting power state to D0, platform_pci_set_power_state()
+	 * ensures main power is on.  If it puts the device in D0, it also
+	 * completes any required delays after the transition; if it leaves
+	 * the device in D1, D2, or D3hot, we use the PM Capability to
+	 * transition to D0.
+	 *
+	 * In all cases, the device is either Configuration-Ready or
+	 * inaccessible upon return.
+	 */
 	platform_pci_set_power_state(dev, PCI_D0);
 
 	if (!dev->pm_cap) {
@@ -1341,10 +1352,19 @@ int pci_power_up(struct pci_dev *dev)
 	pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, 0);
 
 	/* Mandatory transition delays; see PCI PM 1.2. */
-	if (state == PCI_D3hot)
+	if (state == PCI_D3hot) {
 		pci_dev_d3_sleep(dev);
-	else if (state == PCI_D2)
+		if (!(pmcsr & PCI_PM_CTRL_NO_SOFT_RESET)) {
+			ret = pci_dev_wait(dev, "power up D3hot->D0uninitialized",
+					   PCIE_RESET_READY_POLL_MS);
+			if (ret) {
+				dev->current_state = PCI_D3cold;
+				return -EIO;
+			}
+		}
+	} else if (state == PCI_D2) {
 		udelay(PCI_PM_D2_DELAY);
+	}
 
 end:
 	dev->current_state = PCI_D0;
-- 
2.51.0