[RFC 08/10] PCI: qcom: Add support for disabling ASPM L0s in devicetree

[Johan Hovold <johan+linaro@kernel.org>]

A recent commit started enabling ASPM unconditionally when the hardware
claims to support it. This triggers Correctable Errors for some PCIe
devices on machines like the Lenovo ThinkPad X13s, which could indicate
an incomplete driver ASPM implementation or that the hardware does in
fact not support L0s.

Add support for disabling ASPM L0s in the devicetree when it is not
supported on a particular machine and controller.

Note that only the 1.9.0 ops enable ASPM currently.

Fixes: a9a023c05697 ("PCI: qcom: Add support for disabling ASPM L0s in devicetree")
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
 drivers/pci/controller/dwc/pcie-qcom.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
index 2455decc574a..071741b81644 100644
--- a/drivers/pci/controller/dwc/pcie-qcom.c
+++ b/drivers/pci/controller/dwc/pcie-qcom.c
@@ -273,6 +273,25 @@ static int qcom_pcie_start_link(struct dw_pcie *pci)
 	return 0;
 }
 
+static void qcom_pcie_clear_aspm_l0s(struct dw_pcie *pci)
+{
+	u16 offset;
+	u32 val;
+
+	if (!of_property_read_bool(pci->dev->of_node, "aspm-no-l0s"))
+		return;
+
+	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+
+	dw_pcie_dbi_ro_wr_en(pci);
+
+	val = readl(pci->dbi_base + offset + PCI_EXP_LNKCAP);
+	val &= ~PCI_EXP_LNKCAP_ASPM_L0S;
+	writel(val, pci->dbi_base + offset + PCI_EXP_LNKCAP);
+
+	dw_pcie_dbi_ro_wr_dis(pci);
+}
+
 static void qcom_pcie_clear_hpc(struct dw_pcie *pci)
 {
 	u16 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
@@ -962,6 +981,7 @@ static int qcom_pcie_init_2_7_0(struct qcom_pcie *pcie)
 
 static int qcom_pcie_post_init_2_7_0(struct qcom_pcie *pcie)
 {
+	qcom_pcie_clear_aspm_l0s(pcie->pci);
 	qcom_pcie_clear_hpc(pcie->pci);
 
 	return 0;
-- 
2.43.0