PCI: qcom: Add .get_ltssm() callback to query LTSSM status

For older SoCs like SC7280, reading DBI LTSSM register after sending
PME_Turn_Off message causes NOC error.

To avoid unsafe DBI accesses, introduce qcom_pcie_get_ltssm() to retrieve
the LTSSM state without DBI. For newer platforms, read the LTSSM state from
the PARF_LTSSM register; for older platforms continue to retrieve it from
ELBI_SYS_STTS.

This helper is used in place of direct DBI-based link state checks in the
D3cold path after sending PME_Turn_Off message, ensuring the LTSSM state
can be queried safely even after DBI access is no longer valid.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
[mani: commit log and fixed get_ltssm() check]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260429-d3cold-v5-2-89e9735b9df6@oss.qualcomm.com

1 files changed, 31 insertions, 0 deletions

diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
index f21f3806fc1f..881746efe3b6 100644
--- a/drivers/pci/controller/dwc/pcie-qcom.c
+++ b/drivers/pci/controller/dwc/pcie-qcom.c
@@ -71,6 +71,7 @@
 
 /* ELBI registers */
 #define ELBI_SYS_CTRL				0x04
+#define ELBI_SYS_STTS				0x08
 
 /* DBI registers */
 #define AXI_MSTR_RESP_COMP_CTRL0		0x818
@@ -131,6 +132,7 @@
 
 /* PARF_LTSSM register fields */
 #define LTSSM_EN				BIT(8)
+#define PARF_LTSSM_STATE_MASK			GENMASK(5, 0)
 
 /* PARF_NO_SNOOP_OVERRIDE register fields */
 #define WR_NO_SNOOP_OVERRIDE_EN			BIT(1)
@@ -145,6 +147,9 @@
 /* ELBI_SYS_CTRL register fields */
 #define ELBI_SYS_CTRL_LT_ENABLE			BIT(0)
 
+/* ELBI_SYS_STTS register fields */
+#define ELBI_SYS_STTS_LTSSM_STATE_MASK		GENMASK(17, 12)
+
 /* AXI_MSTR_RESP_COMP_CTRL0 register fields */
 #define CFG_REMOTE_RD_REQ_BRIDGE_SIZE_2K	0x4
 #define CFG_REMOTE_RD_REQ_BRIDGE_SIZE_4K	0x5
@@ -245,6 +250,7 @@ struct qcom_pcie_ops {
 	void (*deinit)(struct qcom_pcie *pcie);
 	void (*ltssm_enable)(struct qcom_pcie *pcie);
 	int (*config_sid)(struct qcom_pcie *pcie);
+	enum dw_pcie_ltssm (*get_ltssm)(struct qcom_pcie *pcie);
 };
 
  /**
@@ -428,6 +434,15 @@ static void qcom_pcie_2_1_0_ltssm_enable(struct qcom_pcie *pcie)
 	writel(val, pci->elbi_base + ELBI_SYS_CTRL);
 }
 
+static enum dw_pcie_ltssm qcom_pcie_2_1_0_get_ltssm(struct qcom_pcie *pcie)
+{
+	struct dw_pcie *pci = pcie->pci;
+	u32 val;
+
+	val = readl(pci->elbi_base + ELBI_SYS_STTS);
+	return (enum dw_pcie_ltssm)FIELD_GET(ELBI_SYS_STTS_LTSSM_STATE_MASK, val);
+}
+
 static int qcom_pcie_get_resources_2_1_0(struct qcom_pcie *pcie)
 {
 	struct qcom_pcie_resources_2_1_0 *res = &pcie->res.v2_1_0;
@@ -1260,6 +1275,19 @@ static bool qcom_pcie_link_up(struct dw_pcie *pci)
 	return val & PCI_EXP_LNKSTA_DLLLA;
 }
 
+static enum dw_pcie_ltssm qcom_pcie_get_ltssm(struct dw_pcie *pci)
+{
+	struct qcom_pcie *pcie = to_qcom_pcie(pci);
+	u32 val;
+
+	if (pcie->cfg->ops->get_ltssm)
+		return pcie->cfg->ops->get_ltssm(pcie);
+
+	val = readl(pcie->parf + PARF_LTSSM);
+
+	return (enum dw_pcie_ltssm)FIELD_GET(PARF_LTSSM_STATE_MASK, val);
+}
+
 static void qcom_pcie_phy_power_off(struct qcom_pcie *pcie)
 {
 	struct qcom_pcie_port *port;
@@ -1385,6 +1413,7 @@ static const struct qcom_pcie_ops ops_2_1_0 = {
 	.post_init = qcom_pcie_post_init_2_1_0,
 	.deinit = qcom_pcie_deinit_2_1_0,
 	.ltssm_enable = qcom_pcie_2_1_0_ltssm_enable,
+	.get_ltssm = qcom_pcie_2_1_0_get_ltssm,
 };
 
 /* Qcom IP rev.: 1.0.0	Synopsys IP rev.: 4.11a */
@@ -1394,6 +1423,7 @@ static const struct qcom_pcie_ops ops_1_0_0 = {
 	.post_init = qcom_pcie_post_init_1_0_0,
 	.deinit = qcom_pcie_deinit_1_0_0,
 	.ltssm_enable = qcom_pcie_2_1_0_ltssm_enable,
+	.get_ltssm = qcom_pcie_2_1_0_get_ltssm,
 };
 
 /* Qcom IP rev.: 2.3.2	Synopsys IP rev.: 4.21a */
@@ -1512,6 +1542,7 @@ static const struct qcom_pcie_cfg cfg_fw_managed = {
 static const struct dw_pcie_ops dw_pcie_ops = {
 	.link_up = qcom_pcie_link_up,
 	.start_link = qcom_pcie_start_link,
+	.get_ltssm = qcom_pcie_get_ltssm,
 };
 
 static int qcom_pcie_icc_init(struct qcom_pcie *pcie)