[PATCH v4 2/5] PCI: qcom: Add .get_ltssm() helper

Krishna Chaitanya Chundru
2026-04-07T13:03:39Z

For older targets like sc7280, we see reading DBI after sending PME
turn off message is causing NOC error.

To avoid unsafe DBI accesses, introduce qcom_pcie_get_ltssm(), which
retrieves the LTSSM state from the PARF_LTSSM register instead.

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state can be queried safely even after DBI access is no longer valid.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>
---
drivers/pci/controller/dwc/pcie-qcom.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
index 67a16af69ddc75fca1b123e70715e692a91a9135..b00bf46637a5ff803a845719c5b0b5b82739244b 100644
--- a/drivers/pci/controller/dwc/pcie-qcom.c
+++ b/drivers/pci/controller/dwc/pcie-qcom.c
@@ -131,6 +131,7 @@

/* 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)
@@ -1255,6 +1256,16 @@ 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;
+
+ 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;
@@ -1507,6 +1518,7 @@ 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)

--
2.34.1