Re: [RFC PATCH v2] PCI: Only enable IO window if supported

[Yinghai Lu <yinghai@kernel.org>]

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On Wed, Jul 29, 2015 at 1:26 PM, Bjorn Helgaas <bhelgaas@google.com> wrote:
> On Wed, Jul 29, 2015 at 01:02:25PM -0700, Guenter Roeck wrote:
>> Bjorn, how do you want to handle the flag problem ?
>> Do you have an idea on how to make it work with
>> the reversed definition ?
>
> I'll wait for the revised patch.  Sorry for screwing this up.

Please check attached updated version.

Yinghai

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commit 4b59da521f7e0aedff75c2aa90b6a653727cdf7f
Author: Guenter Roeck <linux@roeck-us.net>
Date:   Tue Jul 7 11:11:20 2015 -0700

    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.
    
    [bhelgaas: reverse sense of new pci_bus_flags_t value]
    [yinghai: simplify root bus flag check, fix flags initial setting, change to bool]
    Signed-off-by: Guenter Roeck <linux@roeck-us.net>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

---
 drivers/pci/probe.c     |   51 ++++++++++++++++++++++++++++++++++++++++++++++++
 drivers/pci/setup-bus.c |   11 ++--------
 include/linux/pci.h     |    1 
 3 files changed, 55 insertions(+), 8 deletions(-)

Index: linux-2.6/drivers/pci/probe.c
===================================================================
--- linux-2.6.orig/drivers/pci/probe.c
+++ linux-2.6/drivers/pci/probe.c
@@ -332,6 +332,32 @@ static void pci_read_bases(struct pci_de
 	}
 }
 
+static bool pci_bridge_supports_io(struct pci_dev *bridge)
+{
+	u16 io;
+
+	pci_read_config_word(bridge, PCI_IO_BASE, &io);
+	if (io)
+		return true;
+
+	/* 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 true;
+
+	return false;
+}
+
+static bool pci_root_has_io_resource(struct pci_bus *bus)
+{
+	while (bus->parent)
+		bus = bus->parent;
+
+	return !!(bus->bus_flags & PCI_BUS_FLAGS_SUPPORTS_IO);
+}
+
 static void pci_read_bridge_io(struct pci_bus *child)
 {
 	struct pci_dev *dev = child->self;
@@ -340,6 +366,21 @@ static void pci_read_bridge_io(struct pc
 	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;
+	}
+
+	if (!pci_root_has_io_resource(child)) {
+		dev_printk(KERN_DEBUG, &dev->dev, "  no I/O resource on root bus\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 +537,7 @@ static struct pci_bus *pci_alloc_bus(str
 	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;
@@ -2058,6 +2100,15 @@ int pci_bus_insert_busn_res(struct pci_b
 		res->flags |= IORESOURCE_PCI_FIXED;
 	}
 
+	b->bus_flags &= ~PCI_BUS_FLAGS_SUPPORTS_IO;
+	resource_list_for_each_entry(window, &bridge->windows) {
+		res = window->res;
+		if (resource_type(res) == IORESOURCE_IO) {
+			b->bus_flags |= PCI_BUS_FLAGS_SUPPORTS_IO;
+			break;
+		}
+	}
+
 	conflict = request_resource_conflict(parent_res, res);
 
 	if (conflict)
Index: linux-2.6/drivers/pci/setup-bus.c
===================================================================
--- linux-2.6.orig/drivers/pci/setup-bus.c
+++ linux-2.6/drivers/pci/setup-bus.c
@@ -744,7 +744,6 @@ int pci_claim_bridge_resource(struct pci
    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;
@@ -752,14 +751,10 @@ static void pci_bridge_check_ranges(stru
 	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;
+	else
+		b_res[0].flags &= ~IORESOURCE_IO;
 
 	/*  DECchip 21050 pass 2 errata: the bridge may miss an address
 	    disconnect boundary by one PCI data phase.
Index: linux-2.6/include/linux/pci.h
===================================================================
--- linux-2.6.orig/include/linux/pci.h
+++ linux-2.6/include/linux/pci.h
@@ -193,6 +193,7 @@ typedef unsigned short __bitwise pci_bus
 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 */