PCI: dwc: Add missing PCI_EXP_LNKCAP_MLW handling

Update dw_pcie_link_set_max_link_width() to set PCI_EXP_LNKCAP_MLW.

In accordance with the DW PCIe RC/EP HW manuals [1,2,3,...] aside with
the PORT_LINK_CTRL_OFF.LINK_CAPABLE and GEN2_CTRL_OFF.NUM_OF_LANES[8:0]
field there is another one which needs to be updated.

It's LINK_CAPABILITIES_REG.PCIE_CAP_MAX_LINK_WIDTH. If it isn't done at
the very least the maximum link-width capability CSR won't expose the
actual maximum capability.

[1] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
    Version 4.60a, March 2015, p.1032
[2] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
    Version 4.70a, March 2016, p.1065
[3] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
    Version 4.90a, March 2016, p.1057
...
[X] DesignWare Cores PCI Express Controller Databook - DWC PCIe Endpoint,
      Version 5.40a, March 2019, p.1396
[X+1] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
      Version 5.40a, March 2019, p.1266

Suggested-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/linux-pci/20231018085631.1121289-4-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>

Author: shimoday

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

@@ -734,7 +734,8 @@ static void dw_pcie_link_set_max_speed(struct dw_pcie *pci, u32 link_gen)
 
 static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes)
 {
-	u32 lwsc, plc;
+	u32 lnkcap, lwsc, plc;
+	u8 cap;
 
 	if (!num_lanes)
 		return;
@@ -770,6 +771,12 @@ static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes)
 	}
 	dw_pcie_writel_dbi(pci, PCIE_PORT_LINK_CONTROL, plc);
 	dw_pcie_writel_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL, lwsc);
+
+	cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+	lnkcap = dw_pcie_readl_dbi(pci, cap + PCI_EXP_LNKCAP);
+	lnkcap &= ~PCI_EXP_LNKCAP_MLW;
+	lnkcap |= FIELD_PREP(PCI_EXP_LNKCAP_MLW, num_lanes);
+	dw_pcie_writel_dbi(pci, cap + PCI_EXP_LNKCAP, lnkcap);
 }
 
 void dw_pcie_iatu_detect(struct dw_pcie *pci)