PCI: dwc: Update pci->num_lanes to maximum supported link width

If the num-lanes property is not present in the devicetree, update
pci->num_lanes with the hardware supported maximum link width using
the newly introduced dw_pcie_link_get_max_link_width() API.

The API is used to get the Maximum Link Width (MLW) of the controller.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
[mani: reworded commit message a bit]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://patch.msgid.link/20250328-preset_v6-v9-3-22cfa0490518@oss.qualcomm.com

Author: krishnachaitanya-linux

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

@@ -523,6 +523,9 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
 
 	dw_pcie_iatu_detect(pci);
 
+	if (pci->num_lanes < 1)
+		pci->num_lanes = dw_pcie_link_get_max_link_width(pci);
+
 	/*
 	 * Allocate the resource for MSG TLP before programming the iATU
 	 * outbound window in dw_pcie_setup_rc(). Since the allocation depends

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

@@ -781,6 +781,14 @@ static void dw_pcie_link_set_max_speed(struct dw_pcie *pci)
 
 }
 
+int dw_pcie_link_get_max_link_width(struct dw_pcie *pci)
+{
+	u8 cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+	u32 lnkcap = dw_pcie_readl_dbi(pci, cap + PCI_EXP_LNKCAP);
+
+	return FIELD_GET(PCI_EXP_LNKCAP_MLW, lnkcap);
+}
+
 static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes)
 {
 	u32 lnkcap, lwsc, plc;

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

@@ -540,6 +540,7 @@ void dw_pcie_write_dbi2(struct dw_pcie *pci, u32 reg, size_t size, u32 val);
 int dw_pcie_link_up(struct dw_pcie *pci);
 void dw_pcie_upconfig_setup(struct dw_pcie *pci);
 int dw_pcie_wait_for_link(struct dw_pcie *pci);
+int dw_pcie_link_get_max_link_width(struct dw_pcie *pci);
 int dw_pcie_prog_outbound_atu(struct dw_pcie *pci,
 			      const struct dw_pcie_ob_atu_cfg *atu);
 int dw_pcie_prog_inbound_atu(struct dw_pcie *pci, int index, int type,