[PATCH v3] PCI: Only enable IO window if supported

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The PCI subsystem always assumes that I/O is supported on PCIe bridges
and tries to assign an I/O window to each child bus 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 bus or its parent does not support I/O in
the first place.

To avoid this message, check if a bus supports I/O before trying to enable
it.  Also check if the root bus has an IO window assigned; if not, it does
not make sense to try to assign one to any of its child busses.

Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
v3: Reverse order of new flag, and name it PCI_BUS_FLAGS_SUPPORTS_IO
    instead of PCI_BUS_FLAGS_NO_IO.
    Don't use bool in pci_bridge_supports_io.
    Drop pci_root_has_io_resource(). Instead, determine if the root bus
    has an io window in pci_create_root_bus(), and clear
    PCI_BUS_FLAGS_SUPPORTS_IO in its bus flags if it doesn't.

v2: Use a new bus flag to indicate if IO is supported on a bus or not.
    Using IORESOURCE_DISABLED in resource flags turned out to be futile,
    since the term "!res->flags" is widely used to detect if a resource
    window is enabled or not, and setting IORESOURCE_DISABLED would
    affect all this code.

This patch depends on 'PCI: move pci_read_bridge_bases to the generic
PCI layer' by Lorenzo Pieralisi; without it, pci_read_bridge_io()
is not always called.
---
 drivers/pci/probe.c     | 34 ++++++++++++++++++++++++++++++++++
 drivers/pci/setup-bus.c |  9 +--------
 include/linux/pci.h     |  1 +
 3 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index cefd636681b6..d9e02ba34035 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -332,6 +332,24 @@ static void pci_read_bases(struct pci_dev *dev, unsigned int howmany, int rom)
 	}
 }
 
+static int pci_bridge_supports_io(struct pci_dev *bridge)
+{
+	u16 io;
+
+	pci_read_config_word(bridge, PCI_IO_BASE, &io);
+	if (io)
+		return 1;
+
+	/* IO_BASE/LIMIT is either hard-wired to zero or programmed to zero */
+	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)
+		return 1;
+
+	return 0;
+}
+
 static void pci_read_bridge_io(struct pci_bus *child)
 {
 	struct pci_dev *dev = child->self;
@@ -340,6 +358,15 @@ static void pci_read_bridge_io(struct pci_bus *child)
 	struct pci_bus_region region;
 	struct resource *res;
 
+	if (!(child->bus_flags & PCI_BUS_FLAGS_SUPPORTS_IO))
+		return;
+
+	if (!pci_bridge_supports_io(dev)) {
+		dev_printk(KERN_DEBUG, &dev->dev, "  no I/O window\n");
+		child->bus_flags &= ~PCI_BUS_FLAGS_SUPPORTS_IO;
+		return;
+	}
+
 	io_mask = PCI_IO_RANGE_MASK;
 	io_granularity = 0x1000;
 	if (dev->io_window_1k) {
@@ -496,6 +523,7 @@ static struct pci_bus *pci_alloc_bus(struct pci_bus *parent)
 	INIT_LIST_HEAD(&b->resources);
 	b->max_bus_speed = PCI_SPEED_UNKNOWN;
 	b->cur_bus_speed = PCI_SPEED_UNKNOWN;
+	b->bus_flags = PCI_BUS_FLAGS_SUPPORTS_IO;
 #ifdef CONFIG_PCI_DOMAINS_GENERIC
 	if (parent)
 		b->domain_nr = parent->domain_nr;
@@ -1938,6 +1966,7 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
 	resource_size_t offset;
 	char bus_addr[64];
 	char *fmt;
+	bool has_io = false;
 
 	b = pci_alloc_bus(NULL);
 	if (!b)
@@ -2016,8 +2045,13 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
 		} else
 			bus_addr[0] = '\0';
 		dev_info(&b->dev, "root bus resource %pR%s\n", res, bus_addr);
+		if (resource_type(res) == IORESOURCE_IO)
+			has_io = true;
 	}
 
+	if (!has_io)
+		b->bus_flags &= ~PCI_BUS_FLAGS_SUPPORTS_IO;
+
 	down_write(&pci_bus_sem);
 	list_add_tail(&b->node, &pci_root_buses);
 	up_write(&pci_bus_sem);
diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 508cc56130e3..c3fdace30faf 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -744,7 +744,6 @@ int pci_claim_bridge_resource(struct pci_dev *bridge, int i)
    base/limit registers must be read-only and read as 0. */
 static void pci_bridge_check_ranges(struct pci_bus *bus)
 {
-	u16 io;
 	u32 pmem;
 	struct pci_dev *bridge = bus->self;
 	struct resource *b_res;
@@ -752,13 +751,7 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
 	b_res = &bridge->resource[PCI_BRIDGE_RESOURCES];
 	b_res[1].flags |= IORESOURCE_MEM;
 
-	pci_read_config_word(bridge, PCI_IO_BASE, &io);
-	if (!io) {
-		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 (bus->bus_flags & PCI_BUS_FLAGS_SUPPORTS_IO)
 		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 8a0321a8fb59..3bbabf344bfc 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -191,6 +191,7 @@ typedef unsigned short __bitwise pci_bus_flags_t;
 enum pci_bus_flags {
 	PCI_BUS_FLAGS_NO_MSI   = (__force pci_bus_flags_t) 1,
 	PCI_BUS_FLAGS_NO_MMRBC = (__force pci_bus_flags_t) 2,
+	PCI_BUS_FLAGS_SUPPORTS_IO = (__force pci_bus_flags_t) 4,
 };
 
 /* These values come from the PCI Express Spec */
-- 
2.1.4

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