PCI: qcom: Add ICC bandwidth vote for CPU to PCIe path

To access the host controller registers of the host controller and the
endpoint BAR/config space, the CPU-PCIe ICC (interconnect) path should
be voted otherwise it may lead to NoC (Network on chip) timeout.
We are surviving because of other driver voting for this path.

As there is less access on this path compared to PCIe to mem path
add minimum vote i.e 1KBps bandwidth always which is sufficient enough
to keep the path active and is recommended by HW team.

During S2RAM (Suspend-to-RAM), the DBI access can happen very late (while
disabling the boot CPU). So do not disable the CPU-PCIe interconnect path
during S2RAM as that may lead to NoC error.

Link: https://lore.kernel.org/linux-pci/20240619-opp_support-v15-1-aa769a2173a3@quicinc.comSigned-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

drivers/pci/controller/dwc/pcie-qcom.c

@@ -255,6 +255,7 @@ struct qcom_pcie {
 	struct phy *phy;
 	struct gpio_desc *reset;
 	struct icc_path *icc_mem;
+	struct icc_path *icc_cpu;
 	const struct qcom_pcie_cfg *cfg;
 	struct dentry *debugfs;
 	bool suspended;
@@ -1371,6 +1372,9 @@ static int qcom_pcie_icc_init(struct qcom_pcie *pcie)
 	if (IS_ERR(pcie->icc_mem))
 		return PTR_ERR(pcie->icc_mem);
 
+	pcie->icc_cpu = devm_of_icc_get(pci->dev, "cpu-pcie");
+	if (IS_ERR(pcie->icc_cpu))
+		return PTR_ERR(pcie->icc_cpu);
 	/*
 	 * Some Qualcomm platforms require interconnect bandwidth constraints
 	 * to be set before enabling interconnect clocks.
@@ -1380,11 +1384,25 @@ static int qcom_pcie_icc_init(struct qcom_pcie *pcie)
 	 */
 	ret = icc_set_bw(pcie->icc_mem, 0, QCOM_PCIE_LINK_SPEED_TO_BW(1));
 	if (ret) {
-		dev_err(pci->dev, "failed to set interconnect bandwidth: %d\n",
+		dev_err(pci->dev, "Failed to set bandwidth for PCIe-MEM interconnect path: %d\n",
 			ret);
 		return ret;
 	}
 
+	/*
+	 * Since the CPU-PCIe path is only used for activities like register
+	 * access of the host controller and endpoint Config/BAR space access,
+	 * HW team has recommended to use a minimal bandwidth of 1KBps just to
+	 * keep the path active.
+	 */
+	ret = icc_set_bw(pcie->icc_cpu, 0, kBps_to_icc(1));
+	if (ret) {
+		dev_err(pci->dev, "Failed to set bandwidth for CPU-PCIe interconnect path: %d\n",
+			ret);
+		icc_set_bw(pcie->icc_mem, 0, 0);
+		return ret;
+	}
+
 	return 0;
 }
 
@@ -1410,7 +1428,7 @@ static void qcom_pcie_icc_update(struct qcom_pcie *pcie)
 
 	ret = icc_set_bw(pcie->icc_mem, 0, width * QCOM_PCIE_LINK_SPEED_TO_BW(speed));
 	if (ret) {
-		dev_err(pci->dev, "failed to set interconnect bandwidth: %d\n",
+		dev_err(pci->dev, "Failed to set bandwidth for PCIe-MEM interconnect path: %d\n",
 			ret);
 	}
 }
@@ -1572,7 +1590,7 @@ static int qcom_pcie_suspend_noirq(struct device *dev)
 	 */
 	ret = icc_set_bw(pcie->icc_mem, 0, kBps_to_icc(1));
 	if (ret) {
-		dev_err(dev, "Failed to set interconnect bandwidth: %d\n", ret);
+		dev_err(dev, "Failed to set bandwidth for PCIe-MEM interconnect path: %d\n", ret);
 		return ret;
 	}
 
@@ -1596,7 +1614,18 @@ static int qcom_pcie_suspend_noirq(struct device *dev)
 		pcie->suspended = true;
 	}
 
-	return 0;
+	/*
+	 * Only disable CPU-PCIe interconnect path if the suspend is non-S2RAM.
+	 * Because on some platforms, DBI access can happen very late during the
+	 * S2RAM and a non-active CPU-PCIe interconnect path may lead to NoC
+	 * error.
+	 */
+	if (pm_suspend_target_state != PM_SUSPEND_MEM) {
+		ret = icc_disable(pcie->icc_cpu);
+		if (ret)
+			dev_err(dev, "Failed to disable CPU-PCIe interconnect path: %d\n", ret);
+	}
+	return ret;
 }
 
 static int qcom_pcie_resume_noirq(struct device *dev)
@@ -1604,6 +1633,14 @@ static int qcom_pcie_resume_noirq(struct device *dev)
 	struct qcom_pcie *pcie = dev_get_drvdata(dev);
 	int ret;
 
+	if (pm_suspend_target_state != PM_SUSPEND_MEM) {
+		ret = icc_enable(pcie->icc_cpu);
+		if (ret) {
+			dev_err(dev, "Failed to enable CPU-PCIe interconnect path: %d\n", ret);
+			return ret;
+		}
+	}
+
 	if (pcie->suspended) {
 		ret = qcom_pcie_host_init(&pcie->pci->pp);
 		if (ret)