PCI: sophgo: Disable L0s and L1 on Sophgo 2044 PCIe Root Ports

Sophgo 2044 Root Ports advertise L0 and L1 capabilities without supporting
them. Since commit f3ac2ff ("PCI/ASPM: Enable all ClockPM and ASPM
states for devicetree platforms") force enabled ASPM on all device tree
platforms, the issue became evident and the SG2044 Root Port started
breaking.

Hence, disable the L0s and L1 capabilities in the LINKCAP register for the
SG2044 Root Ports, so that these states won't get enabled.

Fixes: 467d9c0 ("PCI: dwc: Add Sophgo SG2044 PCIe controller driver in Root Complex mode")
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
[mani: reworded description and corrected fixes tag]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Tested-by: Han Gao <gaohan@iscas.ac.cn>
Link: https://patch.msgid.link/20260109040756.731169-1-inochiama@gmail.com

Author: inochisa

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

@@ -161,6 +161,22 @@ static void sophgo_pcie_msi_enable(struct dw_pcie_rp *pp)
 	raw_spin_unlock_irqrestore(&pp->lock, flags);
 }
 
+static void sophgo_pcie_disable_l0s_l1(struct dw_pcie_rp *pp)
+{
+	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
+	u32 offset, val;
+
+	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+
+	dw_pcie_dbi_ro_wr_en(pci);
+
+	val = dw_pcie_readl_dbi(pci, PCI_EXP_LNKCAP + offset);
+	val &= ~(PCI_EXP_LNKCAP_ASPM_L0S | PCI_EXP_LNKCAP_ASPM_L1);
+	dw_pcie_writel_dbi(pci, PCI_EXP_LNKCAP + offset, val);
+
+	dw_pcie_dbi_ro_wr_dis(pci);
+}
+
 static int sophgo_pcie_host_init(struct dw_pcie_rp *pp)
 {
 	int irq;
@@ -171,6 +187,8 @@ static int sophgo_pcie_host_init(struct dw_pcie_rp *pp)
 
 	irq_set_chained_handler_and_data(irq, sophgo_pcie_intx_handler, pp);
 
+	sophgo_pcie_disable_l0s_l1(pp);
+
 	sophgo_pcie_msi_enable(pp);
 
 	return 0;