linux-kernel - [PATCH] PCI: Allow PCI express root ports to find themselves

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Date:   Thu, 17 Aug 2017 13:06:14 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     David Miller <davem@...emloft.net>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Ding Tianhong <dingtianhong@...wei.com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     leedom@...lsio.com, ashok.raj@...el.com, werner@...lsio.com,
        ganeshgr@...lsio.com, asit.k.mallick@...el.com,
        patrick.j.cramer@...el.com, Suravee.Suthikulpanit@....com,
        Bob.Shaw@....com, l.stach@...gutronix.de, amira@...lanox.com,
        gabriele.paoloni@...wei.com, David.Laight@...lab.com,
        jeffrey.t.kirsher@...el.com, catalin.marinas@....com,
        will.deacon@....com, mark.rutland@....com, robin.murphy@....com,
        alexander.duyck@...il.com, eric.dumazet@...il.com,
        linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com
Subject: [PATCH] PCI: Allow PCI express root ports to find themselves

From: Thierry Reding <treding@...dia.com>

If the pci_find_pcie_root_port() function is called on a root port
itself, return the root port rather than NULL.

This effectively reverts commit 0e405232871d6 ("PCI: fix oops when
try to find Root Port for a PCI device") which added an extra check
that would now be redundant.

Fixes: a99b646afa8a ("PCI: Disable PCIe Relaxed Ordering if unsupported")
Fixes: c56d4450eb68 ("PCI: Turn off Request Attributes to avoid Chelsio T5 Completion erratum")
Signed-off-by: Thierry Reding <treding@...dia.com>
---
This applies on top of and was tested on next-20170817.

Michael, it'd be great if you could test this one again to clarify
whether or not the fix that's already in Linus' tree is still needed, or
whether it's indeed obsoleted by this patch.

 drivers/pci/pci.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b05c587e335a..dd56c1c05614 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -514,7 +514,7 @@ EXPORT_SYMBOL(pci_find_resource);
  */
 struct pci_dev *pci_find_pcie_root_port(struct pci_dev *dev)
 {
-	struct pci_dev *bridge, *highest_pcie_bridge = NULL;
+	struct pci_dev *bridge, *highest_pcie_bridge = dev;
 
 	bridge = pci_upstream_bridge(dev);
 	while (bridge && pci_is_pcie(bridge)) {
@@ -522,11 +522,10 @@ struct pci_dev *pci_find_pcie_root_port(struct pci_dev *dev)
 		bridge = pci_upstream_bridge(bridge);
 	}
 
-	if (highest_pcie_bridge &&
-	    pci_pcie_type(highest_pcie_bridge) == PCI_EXP_TYPE_ROOT_PORT)
-		return highest_pcie_bridge;
+	if (pci_pcie_type(highest_pcie_bridge) != PCI_EXP_TYPE_ROOT_PORT)
+		return NULL;
 
-	return NULL;
+	return highest_pcie_bridge;
 }
 EXPORT_SYMBOL(pci_find_pcie_root_port);
 
-- 
2.13.3