linux-kernel - [PATCH v1 2/2] PCI: dwc: Skip waiting for link up on probe

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Date:   Fri, 24 Feb 2023 13:57:47 -0600
From:   Sajid Dalvi <sdalvi@...gle.com>
To:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        "Krzysztof Wilczyński" <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Sajid Dalvi <sdalvi@...gle.com>, kernel-team@...roid.com,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Andrew Chant <achant@...gle.com>
Subject: [PATCH v1 2/2] PCI: dwc: Skip waiting for link up on probe

When the Root Complex is probed, the default behavior is to spin in a loop
waiting for the link to come up. In some systems the link is not brought up
during probe, but later in the context of an end-point turning on.

Call trace:
dw_pcie_wait_for_link << spins in a loop for 1 second
dw_pcie_host_init

Adding the snps,skip-wait-link-up property in the pcie device tree node
will skip this loop and save 1 second per interface on pcie probe for
systems that do not need to bring up the link this early in the boot
sequence.

Signed-off-by: Sajid Dalvi <sdalvi@...gle.com>
Signed-off-by: Andrew Chant <achant@...gle.com>
---
 drivers/pci/controller/dwc/pcie-designware-host.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 3ab6ae3712c4..f5cba44ebf39 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -477,8 +477,9 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
 			goto err_free_msi;
 	}
 
-	/* Ignore errors, the link may come up later */
-	dw_pcie_wait_for_link(pci);
+	if (!of_property_read_bool(np, "snps,skip-wait-link-up"))
+		/* Ignore errors, the link may come up later */
+		dw_pcie_wait_for_link(pci);
 
 	bridge->sysdata = pp;
 
-- 
2.39.2.637.g21b0678d19-goog