[PATCH v2 1/2] PCI: dwc: Force L2 link entry on shutdown/reboot without D3cold check

[Krishna Chaitanya Chundru]

dw_pcie_suspend_noirq() normally calls pci_host_common_d3cold_possible()
to check whether every downstream endpoint can be put into D3cold before
bothering to move the link to L2. If no endpoint supports it, the
function returns early and leaves the link up.

Querying D3cold support during shutdown is actively harmful, not just
slow: pci_host_common_d3cold_possible() requires every active endpoint
to already be in PCI_D3hot, and returns false otherwise. If any endpoint
is still in D0 -- which is common, since endpoint drivers aren't
guaranteed to have suspended by the time the host's shutdown path runs
the check fails and dw_pcie_suspend_noirq() returns early without ever
moving the link to L2, leaving it up right up to the point where the
system cuts power/clocks to the controller.

Detect the shutdown/reboot case via system_state and skip straight to
forcing the link into L2, the same sequence used for the D3cold-capable
case.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>
---
 drivers/pci/controller/dwc/pcie-designware-host.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 06722259d2e3..98cd9dd2c7d7 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -13,6 +13,7 @@
 #include <linux/irqchip/chained_irq.h>
 #include <linux/irqchip/irq-msi-lib.h>
 #include <linux/irqdomain.h>
+#include <linux/kernel.h>
 #include <linux/msi.h>
 #include <linux/of_address.h>
 #include <linux/of_pci.h>
@@ -1222,16 +1223,29 @@ static int dw_pcie_pme_turn_off(struct dw_pcie *pci)
 
 int dw_pcie_suspend_noirq(struct dw_pcie *pci)
 {
-	bool pme_capable = false;
+	bool shutdown = system_state == SYSTEM_HALT ||
+			system_state == SYSTEM_POWER_OFF ||
+			system_state == SYSTEM_RESTART;
+	bool d3cold, pme_capable = false;
 	int ret = 0;
 	u32 val;
 
 	if (!dw_pcie_link_up(pci))
 		goto stop_link;
 
-	if (!pci_host_common_d3cold_possible(pci->pp.bridge, &pme_capable))
+	/*
+	 * During reboot/halt/poweroff the link is going away regardless, so
+	 * force L2 entry without checking whether endpoints have transitioned
+	 * to D3hot -- there's no point walking the bus to find out.
+	 */
+	if (shutdown)
+		goto d3cold;
+
+	d3cold = pci_host_common_d3cold_possible(pci->pp.bridge, &pme_capable);
+	if (!d3cold)
 		return 0;
 
+d3cold:
 	if (pci->pp.ops->pme_turn_off) {
 		pci->pp.ops->pme_turn_off(&pci->pp);
 	} else {

-- 
2.34.1