linux-kernel - [PATCH v4 1/3] PCI: dwc: Skip waiting for link up if vendor drivers can detect Link up event

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Message-ID: <20241115-remove_wait1-v4-1-7e3412756e3d@quicinc.com>
Date: Fri, 15 Nov 2024 16:00:21 +0530
From: Krishna chaitanya chundru <quic_krichai@...cinc.com>
To: Jingoo Han <jingoohan1@...il.com>,
        Manivannan Sadhasivam
	<manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi
	<lpieralisi@...nel.org>,
        Krzysztof Wilczyński
	<kw@...ux.com>,
        Rob Herring <robh@...nel.org>, Bjorn Helgaas
	<bhelgaas@...gle.com>,
        Konrad Dybcio <konradybcio@...nel.org>
CC: <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>,
        Krzysztof Wilczyński
	<kwilczynski@...nel.org>,
        <quic_vbadigan@...cinc.com>, <quic_mrana@...cinc.com>,
        <andersson@...nel.org>,
        Krishna chaitanya chundru
	<quic_krichai@...cinc.com>
Subject: [PATCH v4 1/3] PCI: dwc: Skip waiting for link up if vendor
 drivers can detect Link up event

If the vendor drivers can detect the Link up event using mechanisms
such as Link up IRQ and can the driver can enumerate downstream devices
instead of waiting here, then waiting for Link up during probe is not
needed here, which optimizes the boot time.

So skip waiting for link to be up if the driver supports 'linkup_irq'.

Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
---
 drivers/pci/controller/dwc/pcie-designware-host.c | 10 ++++++++--
 drivers/pci/controller/dwc/pcie-designware.h      |  1 +
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 3e41865c7290..c8208a6c03d1 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -530,8 +530,14 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
 			goto err_remove_edma;
 	}
 
-	/* Ignore errors, the link may come up later */
-	dw_pcie_wait_for_link(pci);
+	/*
+	 * Note: The link up delay is skipped only when a link up IRQ is present.
+	 * This flag should not be used to bypass the link up delay for arbitrary
+	 * reasons.
+	 */
+	if (!pp->use_linkup_irq)
+		/* Ignore errors, the link may come up later */
+		dw_pcie_wait_for_link(pci);
 
 	bridge->sysdata = pp;
 
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index 347ab74ac35a..1d0ec47e1986 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -379,6 +379,7 @@ struct dw_pcie_rp {
 	bool			use_atu_msg;
 	int			msg_atu_index;
 	struct resource		*msg_res;
+	bool			use_linkup_irq;
 };
 
 struct dw_pcie_ep_ops {

-- 
2.34.1