[PATCH v6 2/2] PCI: update device mps when doing pci hotplug

[Yijing Wang <wangyijing@huawei.com>]

Currently we don't update device's mps value when doing
pci device hot-add. The hot-added device's mps will be set
to default value (128B). But the upstream port device's mps
may be larger than 128B which was set by firmware during
system bootup. In this case the new added device may not
work normally. This patch try to update the hot added device
mps equal to its parent mps, if device mpss < parent mps,
print warning.

References: https://bugzilla.kernel.org/show_bug.cgi?id=60671
Reported-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Cc: Jon Mason <jdmason@kudzu.us>
Cc: stable@vger.kernel.org # 3.4+
---
 drivers/pci/probe.c |   49 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 48 insertions(+), 1 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 160ae38..a18fa3b 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1600,6 +1600,44 @@ static int pcie_bus_configure_set(struct pci_dev *dev, void *data)
 	return 0;
 }
 
+static int pcie_bus_update_set(struct pci_dev *dev, void *data)
+{
+	int mps, p_mps, mpss;
+	struct pci_dev *parent;
+
+	if (!pci_is_pcie(dev) || !dev->bus->self)
+		return 0;
+
+	parent = dev->bus->self;
+	mps = pcie_get_mps(dev);
+	p_mps = pcie_get_mps(dev->bus->self);
+
+	if (mps >= p_mps)
+		return 0;
+
+	/* we only update the device mps, unless its parent device is root port,
+	 * and it is the only slot directly connected to root port.
+	 */
+	mpss = 128 << dev->pcie_mpss;
+	if (mpss >= p_mps) {
+		pcie_write_mps(dev, p_mps);
+	} else if (pci_pcie_type(parent) == PCI_EXP_TYPE_ROOT_PORT &&
+			pci_only_one_slot(dev->bus)) {
+		pcie_write_mps(parent, mpss);
+		pcie_write_mps(dev, mpss);
+	} else
+		dev_warn(&dev->dev, "MPS %d MPSS %d both smaller than upstream MPS %d\n"
+				"If necessary, use \"pci=pcie_bus_peer2peer\" boot parameter to avoid this problem\n",
+				mps, 128 << dev->pcie_mpss, p_mps);
+	return 0;
+}
+
+static void pcie_bus_update_setting(struct pci_bus *bus)
+{
+	if (bus->self->is_hotplug_bridge)
+		pci_walk_bus(bus, pcie_bus_update_set, NULL);
+}
+
 /* pcie_bus_configure_settings requires that pci_walk_bus work in a top-down,
  * parents then children fashion.  If this changes, then this code will not
  * work as designed.
@@ -1611,8 +1649,17 @@ void pcie_bus_configure_settings(struct pci_bus *bus, u8 mpss)
 	if (!pci_is_pcie(bus->self))
 		return;
 
-	if (pcie_bus_config == PCIE_BUS_TUNE_OFF)
+	if (pcie_bus_config == PCIE_BUS_TUNE_OFF) {
+		/* Sometimes we should update device mps here,
+		 * eg. after hot add, device mps value will be
+		 * set to default(128B), but the upstream port
+		 * mps value may be larger than 128B, if we do
+		 * not update the device mps, it maybe can not
+		 * work normally.
+		 */
+		pcie_bus_update_setting(bus);
 		return;
+	}
 
 	/* FIXME - Peer to peer DMA is possible, though the endpoint would need
 	 * to be aware to the MPS of the destination.  To work around this,
-- 
1.7.1