linux-kernel - [PATCH V5 1/1] Intel Sky Lake-E host root ports check.

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Message-Id: <20220331073539.14499-2-shlomop@pliops.com>
Date:   Thu, 31 Mar 2022 10:35:39 +0300
From:   Shlomo Pongratz <shlomopongratz@...il.com>
To:     linux-pci@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, andrew.maier@...eticom.com,
        logang@...tatee.com, bhelgaas@...gle.com, jgg@...dia.com,
        helgaas@...nel.org, Shlomo Pongratz <shlomop@...ops.com>
Subject: [PATCH V5 1/1] Intel Sky Lake-E host root ports check.

In commit 7b94b53db34f ("PCI/P2PDMA: Add Intel Sky Lake-E Root Ports B, C, D to
the whitelist")
Andrew Maier added the Sky Lake-E additional devices
2031, 2032 and 2033 root ports to the already existing 2030 device.

The Intel devices 2030, 2031, 2032 and 2033 which are root ports A, B, C and D,
respectively and if all exist they will occupy slots 0 till 3 in that order.

The original code handled only the case where the devices in the whitelist are
host bridges and assumed that they will be found on slot 0.

This assumption doesn't hold for root ports so an explicit test was added to
cover this case.

Signed-off-by: Shlomo Pongratz <shlomop@...ops.com>
---
 drivers/pci/p2pdma.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 30b1df3c9d2f..87c62ca0976d 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -327,15 +327,18 @@ static const struct pci_p2pdma_whitelist_entry {
 
 /*
  * This lookup function tries to find the PCI device corresponding to a given
- * host bridge.
+ * host bridge or a root port.
  *
  * It assumes the host bridge device is the first PCI device in the
- * bus->devices list and that the devfn is 00.0. These assumptions should hold
- * for all the devices in the whitelist above.
+ * bus->devices list and that the devfn is 00.0. The first assumption should
+ * hold for all the devices in the whitelist above, however the second one
+ * doesn't always holds for root ports, for example Intel SkyLake-E devices
+ * 2030, 2031, 2032 and 2033 which are root ports (A, B, C and D respectively).
+ * So being a root port is checked explicitly.
  *
- * This function is equivalent to pci_get_slot(host->bus, 0), however it does
- * not take the pci_bus_sem lock seeing __host_bridge_whitelist() must not
- * sleep.
+ * This function is equivalent to pci_get_slot(host->bus, 0) (except for
+ * the root port test), however it does not take the pci_bus_sem lock seeing
+ * __host_bridge_whitelist() must not sleep.
  *
  * For this to be safe, the caller should hold a reference to a device on the
  * bridge, which should ensure the host_bridge device will not be freed
@@ -350,7 +353,14 @@ static struct pci_dev *pci_host_bridge_dev(struct pci_host_bridge *host)
 
 	if (!root)
 		return NULL;
-	if (root->devfn != PCI_DEVFN(0, 0))
+
+	/* Verify that the device is a host bridge or a root port
+	 * It is assumed that host bridges have a 0 devfn, (common practice)
+	 * but some of the entries in the whitelist are root ports that can
+	 * have any devfn
+	 */
+	if (root->devfn != PCI_DEVFN(0, 0) &&
+	    pci_pcie_type(root) != PCI_EXP_TYPE_ROOT_PORT)
 		return NULL;
 
 	return root;
-- 
2.17.1