linux-kernel - [PATCH v6 6/9] PCI: qcom: Add support for host_stop_link() & host_start

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Message-Id: <20250828-qps615_v4_1-v6-6-985f90a7dd03@oss.qualcomm.com>
Date: Thu, 28 Aug 2025 17:39:03 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        chaitanya chundru <quic_krichai@...cinc.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        cros-qcom-dts-watchers@...omium.org, Jingoo Han <jingoohan1@...il.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>
Cc: quic_vbadigan@...cnic.com, amitk@...nel.org, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, jorge.ramirez@....qualcomm.com,
        linux-arm-kernel@...ts.infradead.org,
        Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>
Subject: [PATCH v6 6/9] PCI: qcom: Add support for host_stop_link() &
 host_start_link()

Add support for host_stop_link() and host_start_link() for switches like
TC956x, which require configuration before the PCIe link is established.

Assert PERST# and disable LTSSM bit to prevent the PCIe controller from
participating in link training during host_stop_link(). De-assert PERST#
and enable LTSSM bit during host_start_link().

Introduce ltssm_disable function op to stop link training.
For the switches like TC956x, which needs to configure it before
the PCIe link is established.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
---
 drivers/pci/controller/dwc/pcie-qcom.c | 35 ++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
index 294babe1816e4d0c2b2343fe22d89af72afcd6cd..8ec76fbc0787ae305e9c63eb82fbc999d197a123 100644
--- a/drivers/pci/controller/dwc/pcie-qcom.c
+++ b/drivers/pci/controller/dwc/pcie-qcom.c
@@ -250,6 +250,7 @@ struct qcom_pcie_ops {
 	void (*host_post_init)(struct qcom_pcie *pcie);
 	void (*deinit)(struct qcom_pcie *pcie);
 	void (*ltssm_enable)(struct qcom_pcie *pcie);
+	void (*ltssm_disable)(struct qcom_pcie *pcie);
 	int (*config_sid)(struct qcom_pcie *pcie);
 };
 
@@ -642,6 +643,37 @@ static int qcom_pcie_post_init_1_0_0(struct qcom_pcie *pcie)
 	return 0;
 }
 
+static int qcom_pcie_host_start_link(struct dw_pcie *pci)
+{
+	struct qcom_pcie *pcie = to_qcom_pcie(pci);
+
+	qcom_ep_reset_deassert(pcie);
+
+	if (pcie->cfg->ops->ltssm_enable)
+		pcie->cfg->ops->ltssm_enable(pcie);
+
+	return 0;
+}
+
+static void qcom_pcie_host_stop_link(struct dw_pcie *pci)
+{
+	struct qcom_pcie *pcie = to_qcom_pcie(pci);
+
+	qcom_ep_reset_assert(pcie);
+
+	if (pcie->cfg->ops->ltssm_disable)
+		pcie->cfg->ops->ltssm_disable(pcie);
+}
+
+static void qcom_pcie_2_3_2_ltssm_disable(struct qcom_pcie *pcie)
+{
+	u32 val;
+
+	val = readl(pcie->parf + PARF_LTSSM);
+	val &= ~LTSSM_EN;
+	writel(val, pcie->parf + PARF_LTSSM);
+}
+
 static void qcom_pcie_2_3_2_ltssm_enable(struct qcom_pcie *pcie)
 {
 	u32 val;
@@ -1435,6 +1467,7 @@ static const struct qcom_pcie_ops ops_1_9_0 = {
 	.host_post_init = qcom_pcie_host_post_init_2_7_0,
 	.deinit = qcom_pcie_deinit_2_7_0,
 	.ltssm_enable = qcom_pcie_2_3_2_ltssm_enable,
+	.ltssm_disable = qcom_pcie_2_3_2_ltssm_disable,
 	.config_sid = qcom_pcie_config_sid_1_9_0,
 };
 
@@ -1506,6 +1539,8 @@ 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,
+	.host_start_link = qcom_pcie_host_start_link,
+	.host_stop_link = qcom_pcie_host_stop_link,
 };
 
 static int qcom_pcie_icc_init(struct qcom_pcie *pcie)

-- 
2.34.1