PCI: qcom: Enable ASPM for platforms supporting 1.9.0 ops

ASPM is supported by Qcom host controllers/bridges on most of the recent
platforms and so the devices tested so far. But for enabling ASPM by
default (without using Kconfig, kernel command-line or sysfs), BIOS has
to enable ASPM on both host bridge and downstream devices during boot.

Unfortunately, none of the BIOS available on Qcom platforms enables
ASPM. Due to this, the platforms making use of Qcom SoCs draw high power
during runtime.

To fix this power draw issue, users have to enable ASPM using Kconfig,
kernel command-line, sysfs or the BIOS has to start enabling ASPM.

The latter may happen in the future, but that won't address the issue on
current platforms. Also, asking users to enable a feature to get the power
management right would provide an unpleasant out-of-the-box experience.

So the apt solution is to enable ASPM in the controller driver itself. And
this is being accomplished by calling pci_enable_link_state() in the newly
introduced host_post_init() callback for all the devices connected to the
bus. This function enables all supported link low power states for both
host bridge and the downstream devices.

Due to limited testing, ASPM is only enabled for platforms making use of
ops_1_9_0 callbacks.

[kwilczynski: commit log]
Link: https://lore.kernel.org/linux-pci/20231010155914.9516-3-manivannan.sadhasivam@linaro.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

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

@@ -219,6 +219,7 @@ struct qcom_pcie_ops {
 	int (*get_resources)(struct qcom_pcie *pcie);
 	int (*init)(struct qcom_pcie *pcie);
 	int (*post_init)(struct qcom_pcie *pcie);
+	void (*host_post_init)(struct qcom_pcie *pcie);
 	void (*deinit)(struct qcom_pcie *pcie);
 	void (*ltssm_enable)(struct qcom_pcie *pcie);
 	int (*config_sid)(struct qcom_pcie *pcie);
@@ -964,6 +965,22 @@ static int qcom_pcie_post_init_2_7_0(struct qcom_pcie *pcie)
 	return 0;
 }
 
+static int qcom_pcie_enable_aspm(struct pci_dev *pdev, void *userdata)
+{
+	/* Downstream devices need to be in D0 state before enabling PCI PM substates */
+	pci_set_power_state(pdev, PCI_D0);
+	pci_enable_link_state(pdev, PCIE_LINK_STATE_ALL);
+
+	return 0;
+}
+
+static void qcom_pcie_host_post_init_2_7_0(struct qcom_pcie *pcie)
+{
+	struct dw_pcie_rp *pp = &pcie->pci->pp;
+
+	pci_walk_bus(pp->bridge->bus, qcom_pcie_enable_aspm, NULL);
+}
+
 static void qcom_pcie_deinit_2_7_0(struct qcom_pcie *pcie)
 {
 	struct qcom_pcie_resources_2_7_0 *res = &pcie->res.v2_7_0;
@@ -1216,9 +1233,19 @@ static void qcom_pcie_host_deinit(struct dw_pcie_rp *pp)
 	pcie->cfg->ops->deinit(pcie);
 }
 
+static void qcom_pcie_host_post_init(struct dw_pcie_rp *pp)
+{
+	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
+	struct qcom_pcie *pcie = to_qcom_pcie(pci);
+
+	if (pcie->cfg->ops->host_post_init)
+		pcie->cfg->ops->host_post_init(pcie);
+}
+
 static const struct dw_pcie_host_ops qcom_pcie_dw_ops = {
 	.host_init	= qcom_pcie_host_init,
 	.host_deinit	= qcom_pcie_host_deinit,
+	.host_post_init	= qcom_pcie_host_post_init,
 };
 
 /* Qcom IP rev.: 2.1.0	Synopsys IP rev.: 4.01a */
@@ -1280,6 +1307,7 @@ static const struct qcom_pcie_ops ops_1_9_0 = {
 	.get_resources = qcom_pcie_get_resources_2_7_0,
 	.init = qcom_pcie_init_2_7_0,
 	.post_init = qcom_pcie_post_init_2_7_0,
+	.host_post_init = qcom_pcie_host_post_init_2_7_0,
 	.deinit = qcom_pcie_deinit_2_7_0,
 	.ltssm_enable = qcom_pcie_2_3_2_ltssm_enable,
 	.config_sid = qcom_pcie_config_sid_1_9_0,