linux-kernel - [PATCH] PCI: Only enable IO window if supported

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Date:	Fri, 22 May 2015 17:52:16 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH] PCI: Only enable IO window if supported

The PCI subsystem always assumes that I/O is supported on PCIe bridges
and tries to assign an I/O window to each port even if that is not
the case.

This may result in messages such as

pcieport 0000:02:00.0: res[7]=[io  0x1000-0x0fff]
					get_res_add_size add_size 1000
pcieport 0000:02:00.0: BAR 7: no space for [io  size 0x1000]
pcieport 0000:02:00.0: BAR 7: failed to assign [io  size 0x1000]

for each bridge port, even if a port or its parent does not support
I/O in the first place.

To avoid this message, check if a port supports I/O before trying to
enable it. Also check if port's parent supports I/O, and only modify
a port's I/O resource size if both the port and its parent support I/O.

If IO is disabled after the initial port scan, the IO base and size
registers are set to 0x00f0 to indicate that IO is disabled. A later
rescan interprets this as "IO supported" and enables the IO range,
even if the parent does not support IO. Handle this situation as well.

Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
 drivers/pci/probe.c     | 14 ++++++++++++++
 drivers/pci/setup-bus.c |  4 ++--
 include/linux/pci.h     |  9 +++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 6675a7a1b9fc..f4944ef45148 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -354,6 +354,20 @@ static void pci_read_bridge_io(struct pci_bus *child)
 	base = (io_base_lo & io_mask) << 8;
 	limit = (io_limit_lo & io_mask) << 8;
 
+	/* If necessary, check if the bridge supports an I/O aperture */
+	if (!io_base_lo && !io_limit_lo) {
+		u16 io;
+
+		if (!pci_parent_supports_io(child))
+			return;
+
+		pci_write_config_word(dev, PCI_IO_BASE, 0xe0f0);
+		pci_read_config_word(dev, PCI_IO_BASE, &io);
+		pci_write_config_word(dev, PCI_IO_BASE, 0x0);
+		if (!io)
+			return;
+	}
+
 	if ((io_base_lo & PCI_IO_RANGE_TYPE_MASK) == PCI_IO_RANGE_TYPE_32) {
 		u16 io_base_hi, io_limit_hi;
 
diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 4fd0cacf7ca0..963b31a109a9 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -750,12 +750,12 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
 	b_res[1].flags |= IORESOURCE_MEM;
 
 	pci_read_config_word(bridge, PCI_IO_BASE, &io);
-	if (!io) {
+	if (!io && pci_parent_supports_io(bus)) {
 		pci_write_config_word(bridge, PCI_IO_BASE, 0xe0f0);
 		pci_read_config_word(bridge, PCI_IO_BASE, &io);
 		pci_write_config_word(bridge, PCI_IO_BASE, 0x0);
 	}
-	if (io)
+	if (io && (io != 0x00f0 || pci_parent_supports_io(bus)))
 		b_res[0].flags |= IORESOURCE_IO;
 
 	/*  DECchip 21050 pass 2 errata: the bridge may miss an address
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 353db8dc4c6e..f3de9e24aab1 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -489,6 +489,15 @@ static inline bool pci_is_root_bus(struct pci_bus *pbus)
 	return !(pbus->parent);
 }
 
+/*
+ * Returns true if the parent bus supports an I/O aperture.
+ */
+static inline bool pci_parent_supports_io(struct pci_bus *pbus)
+{
+	return pci_is_root_bus(pbus) || pci_is_root_bus(pbus->parent) ||
+	       (pbus->parent->resource[0]->flags & IORESOURCE_IO);
+}
+
 /**
  * pci_is_bridge - check if the PCI device is a bridge
  * @dev: PCI device
-- 
2.1.0

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