linux-kernel - [PATCH v6 3/4] PCI: dwc: Improve handling of PCIe lane configuration

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Message-Id: <20250210-preset_v6-v6-3-cbd837d0028d@oss.qualcomm.com>
Date: Mon, 10 Feb 2025 13:00:02 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, Jingoo Han <jingoohan1@...il.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        quic_mrana@...cinc.com, quic_vbadigan@...cinc.com,
        Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Subject: [PATCH v6 3/4] PCI: dwc: Improve handling of PCIe lane
 configuration

Currently even if the number of lanes hardware supports is equal to
the number lanes provided in the devicetree, the driver is trying to
configure again the maximum number of lanes which is not needed.

Update number of lanes only when it is not equal to hardware capability.

And also if the num-lanes property is not present in the devicetree
update the num_lanes with the maximum hardware supports.

Introduce dw_pcie_link_get_max_link_width() to get the maximum lane
width the hardware supports.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
---
 drivers/pci/controller/dwc/pcie-designware-host.c |  3 +++
 drivers/pci/controller/dwc/pcie-designware.c      | 11 ++++++++++-
 drivers/pci/controller/dwc/pcie-designware.h      |  1 +
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index ffaded8f2df7..dd56cc02f4ef 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -504,6 +504,9 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
 
 	dw_pcie_iatu_detect(pci);
 
+	if (pci->num_lanes < 1)
+		pci->num_lanes = dw_pcie_link_get_max_link_width(pci);
+
 	/*
 	 * Allocate the resource for MSG TLP before programming the iATU
 	 * outbound window in dw_pcie_setup_rc(). Since the allocation depends
diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
index 145e7f579072..967c62cf3db0 100644
--- a/drivers/pci/controller/dwc/pcie-designware.c
+++ b/drivers/pci/controller/dwc/pcie-designware.c
@@ -737,12 +737,21 @@ static void dw_pcie_link_set_max_speed(struct dw_pcie *pci)
 
 }
 
+int dw_pcie_link_get_max_link_width(struct dw_pcie *pci)
+{
+	u8 cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+	u32 lnkcap = dw_pcie_readl_dbi(pci, cap + PCI_EXP_LNKCAP);
+
+	return FIELD_GET(PCI_EXP_LNKCAP_MLW, lnkcap);
+}
+
 static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes)
 {
+	int max_lanes = dw_pcie_link_get_max_link_width(pci);
 	u32 lnkcap, lwsc, plc;
 	u8 cap;
 
-	if (!num_lanes)
+	if (!num_lanes || max_lanes == num_lanes)
 		return;
 
 	/* Set the number of lanes */
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index 501d9ddfea16..61d1fb6b437b 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -488,6 +488,7 @@ void dw_pcie_write_dbi2(struct dw_pcie *pci, u32 reg, size_t size, u32 val);
 int dw_pcie_link_up(struct dw_pcie *pci);
 void dw_pcie_upconfig_setup(struct dw_pcie *pci);
 int dw_pcie_wait_for_link(struct dw_pcie *pci);
+int dw_pcie_link_get_max_link_width(struct dw_pcie *pci);
 int dw_pcie_prog_outbound_atu(struct dw_pcie *pci,
 			      const struct dw_pcie_ob_atu_cfg *atu);
 int dw_pcie_prog_inbound_atu(struct dw_pcie *pci, int index, int type,

-- 
2.34.1