PCI: dwc: Always cache the maximum link speed value in dw_pcie::max_link_speed

Currently, the dw_pcie::max_link_speed has a valid value only if the
controller driver restricts the maximum link speed in the driver or if
the platform does so in the devicetree using the 'max-link-speed'
property.

But having the maximum supported link speed of the platform would be
helpful for the vendor drivers to configure any link specific settings.

So in the case of non-valid value in dw_pcie::max_link_speed, just cache
the hardware default value from Link Capability register.

While at it, remove the 'max_link_speed' argument to the
dw_pcie_link_set_max_speed() function since the value can be
retrieved within the function.

Link: https://lore.kernel.org/linux-pci/20240911-pci-qcom-gen4-stability-v7-2-743f5c1fd027@linaro.orgTested-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Johan Hovold <johan+linaro@kernel.org>

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

@@ -689,16 +689,27 @@ void dw_pcie_upconfig_setup(struct dw_pcie *pci)
 }
 EXPORT_SYMBOL_GPL(dw_pcie_upconfig_setup);
 
-static void dw_pcie_link_set_max_speed(struct dw_pcie *pci, u32 max_link_speed)
+static void dw_pcie_link_set_max_speed(struct dw_pcie *pci)
 {
 	u32 cap, ctrl2, link_speed;
 	u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
 
 	cap = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
+
+	/*
+	 * Even if the platform doesn't want to limit the maximum link speed,
+	 * just cache the hardware default value so that the vendor drivers can
+	 * use it to do any link specific configuration.
+	 */
+	if (pci->max_link_speed < 1) {
+		pci->max_link_speed = FIELD_GET(PCI_EXP_LNKCAP_SLS, cap);
+		return;
+	}
+
 	ctrl2 = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCTL2);
 	ctrl2 &= ~PCI_EXP_LNKCTL2_TLS;
 
-	switch (pcie_link_speed[max_link_speed]) {
+	switch (pcie_link_speed[pci->max_link_speed]) {
 	case PCIE_SPEED_2_5GT:
 		link_speed = PCI_EXP_LNKCTL2_TLS_2_5GT;
 		break;
@@ -1060,8 +1071,7 @@ void dw_pcie_setup(struct dw_pcie *pci)
 {
 	u32 val;
 
-	if (pci->max_link_speed > 0)
-		dw_pcie_link_set_max_speed(pci, pci->max_link_speed);
+	dw_pcie_link_set_max_speed(pci);
 
 	/* Configure Gen1 N_FTS */
 	if (pci->n_fts[0]) {