PCI: dwc: Remove LTSSM state test in dw_pcie_suspend_noirq()

It's safe to send PME_TURN_OFF message regardless of whether the link is up
or down, so don't test the LTSSM state before sending the PME_TURN_OFF
message.

Only print an error message when the LTSSM is not in DETECT or POLL. There
shouldn't be an error when no Endpoint is connected at all.

Link: https://lore.kernel.org/r/20241210081557.163555-3-hongxing.zhu@nxp.com
Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Author: Richard Zhu

drivers/pci/controller/dwc/pcie-designware-host.c

@@ -924,7 +924,7 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
 {
 	u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
 	u32 val;
-	int ret = 0;
+	int ret;
 
 	/*
 	 * If L1SS is supported, then do not put the link into L2 as some
@@ -933,25 +933,32 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
 	if (dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKCTL) & PCI_EXP_LNKCTL_ASPM_L1)
 		return 0;
 
-	if (dw_pcie_get_ltssm(pci) <= DW_PCIE_LTSSM_DETECT_ACT)
-		return 0;
-
-	if (pci->pp.ops->pme_turn_off)
+	if (pci->pp.ops->pme_turn_off) {
 		pci->pp.ops->pme_turn_off(&pci->pp);
-	else
+	} else {
 		ret = dw_pcie_pme_turn_off(pci);
+		if (ret)
+			return ret;
+	}
 
-	if (ret)
-		return ret;
-
-	ret = read_poll_timeout(dw_pcie_get_ltssm, val, val == DW_PCIE_LTSSM_L2_IDLE,
+	ret = read_poll_timeout(dw_pcie_get_ltssm, val,
+				val == DW_PCIE_LTSSM_L2_IDLE ||
+				val <= DW_PCIE_LTSSM_DETECT_WAIT,
 				PCIE_PME_TO_L2_TIMEOUT_US/10,
 				PCIE_PME_TO_L2_TIMEOUT_US, false, pci);
 	if (ret) {
+		/* Only log message when LTSSM isn't in DETECT or POLL */
 		dev_err(pci->dev, "Timeout waiting for L2 entry! LTSSM: 0x%x\n", val);
 		return ret;
 	}
 
+	/*
+	 * Per PCIe r6.0, sec 5.3.3.2.1, software should wait at least
+	 * 100ns after L2/L3 Ready before turning off refclock and
+	 * main power. This is harmless when no endpoint is connected.
+	 */
+	udelay(1);
+
 	dw_pcie_stop_link(pci);
 	if (pci->pp.ops->deinit)
 		pci->pp.ops->deinit(&pci->pp);

drivers/pci/controller/dwc/pcie-designware.h

@@ -330,6 +330,7 @@ enum dw_pcie_ltssm {
 	/* Need to align with PCIE_PORT_DEBUG0 bits 0:5 */
 	DW_PCIE_LTSSM_DETECT_QUIET = 0x0,
 	DW_PCIE_LTSSM_DETECT_ACT = 0x1,
+	DW_PCIE_LTSSM_DETECT_WAIT = 0x6,
 	DW_PCIE_LTSSM_L0 = 0x11,
 	DW_PCIE_LTSSM_L2_IDLE = 0x15,