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Subject[PATCH v3] PCI: avoid bridge feature re-probing on hotplug
I gave up trying to reproduce the problem and test this patch with qemu;
can you guys (Michael and Xu (sorry if I mangled your name)) give this a
try?

I cc'd a few other people who have noticed this issue in the past, so just
FYI for them.

Bjorn


commit dd21b922db366ba069291b6fef2a8ce6768756a2
Author: Bjorn Helgaas <bhelgaas@google.com>
Date: Sat Jan 19 11:35:04 2019 -0600

PCI: Probe bridge window attributes once at enumeration-time

pci_bridge_check_ranges() determines whether a bridge supports the optional
I/O and prefetchable memory windows and sets the flag bits in the bridge
resources. This could be done once during enumeration except that the
resource allocation code completely clears the flag bits, e.g., in the
pci_assign_unassigned_bridge_resources() path.

The problem was that in some cases pci_bridge_check_ranges() *changes* the
window registers to determine whether they're writable, and this may break
concurrent accesses to devices behind the bridge.

Add a new pci_read_bridge_windows() to determine whether a bridge supports
the optional windows, call it once during enumeration, remember the
results, and change pci_bridge_check_ranges() to set the flag bits based on
those remembered results.

Link: https://lore.kernel.org/linux-pci/1506151482-113560-1-git-send-email-wangzhou1@hisilicon.com
Link: https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg02082.html
Reported-by: xuyandong <xuyandong2@huawei.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Ofer Hayut <ofer@lightbitslabs.com>
Cc: Roy Shterman <roys@lightbitslabs.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Zhou Wang <wangzhou1@hisilicon.com>

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 257b9f6f2ebb..2ef8b954c65a 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -348,6 +348,57 @@ static void pci_read_bases(struct pci_dev *dev, unsigned int howmany, int rom)
}
}

+static void pci_read_bridge_windows(struct pci_dev *bridge)
+{
+ u16 io;
+ u32 pmem, tmp;
+
+ 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)
+ bridge->io_window = 1;
+
+ /*
+ * DECchip 21050 pass 2 errata: the bridge may miss an address
+ * disconnect boundary by one PCI data phase. Workaround: do not
+ * use prefetching on this device.
+ */
+ if (bridge->vendor == PCI_VENDOR_ID_DEC && bridge->device == 0x0001)
+ return;
+
+ pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
+ if (!pmem) {
+ pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE,
+ 0xffe0fff0);
+ pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
+ pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE, 0x0);
+ }
+ if (!pmem)
+ return;
+
+ bridge->pref_window = 1;
+
+ if ((pmem & PCI_PREF_RANGE_TYPE_MASK) == PCI_PREF_RANGE_TYPE_64) {
+
+ /*
+ * Bridge claims to have a 64-bit prefetchable memory
+ * window; verify that the upper bits are actually
+ * writable.
+ */
+ pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32, &pmem);
+ pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
+ 0xffffffff);
+ pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32, &tmp);
+ pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32, pmem);
+ if (tmp)
+ bridge->pref_64_window = 1;
+ }
+}
+
static void pci_read_bridge_io(struct pci_bus *child)
{
struct pci_dev *dev = child->self;
@@ -1739,6 +1790,7 @@ int pci_setup_device(struct pci_dev *dev)
pci_read_irq(dev);
dev->transparent = ((dev->class & 0xff) == 1);
pci_read_bases(dev, 2, PCI_ROM_ADDRESS1);
+ pci_read_bridge_windows(dev);
set_pcie_hotplug_bridge(dev);
pos = pci_find_capability(dev, PCI_CAP_ID_SSVID);
if (pos) {
diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index ed960436df5e..1941bb0a6c13 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -735,58 +735,21 @@ 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;
+ struct resource *b_res = &bridge->resource[PCI_BRIDGE_RESOURCES];

- 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 (bridge->io_window)
b_res[0].flags |= IORESOURCE_IO;

- /* DECchip 21050 pass 2 errata: the bridge may miss an address
- disconnect boundary by one PCI data phase.
- Workaround: do not use prefetching on this device. */
- if (bridge->vendor == PCI_VENDOR_ID_DEC && bridge->device == 0x0001)
- return;
-
- pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
- if (!pmem) {
- pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE,
- 0xffe0fff0);
- pci_read_config_dword(bridge, PCI_PREF_MEMORY_BASE, &pmem);
- pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE, 0x0);
- }
- if (pmem) {
+ if (bridge->pref_window) {
b_res[2].flags |= IORESOURCE_MEM | IORESOURCE_PREFETCH;
- if ((pmem & PCI_PREF_RANGE_TYPE_MASK) ==
- PCI_PREF_RANGE_TYPE_64) {
+ if (bridge->pref_64_window) {
b_res[2].flags |= IORESOURCE_MEM_64;
b_res[2].flags |= PCI_PREF_RANGE_TYPE_64;
}
}
-
- /* double check if bridge does support 64 bit pref */
- if (b_res[2].flags & IORESOURCE_MEM_64) {
- u32 mem_base_hi, tmp;
- pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32,
- &mem_base_hi);
- pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
- 0xffffffff);
- pci_read_config_dword(bridge, PCI_PREF_BASE_UPPER32, &tmp);
- if (!tmp)
- b_res[2].flags &= ~IORESOURCE_MEM_64;
- pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32,
- mem_base_hi);
- }
}

/* Helper function for sizing routines: find first available
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 65f1d8c2f082..40b327b814aa 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -373,6 +373,9 @@ struct pci_dev {
bool match_driver; /* Skip attaching driver */

unsigned int transparent:1; /* Subtractive decode bridge */
+ unsigned int io_window:1; /* Bridge has I/O window */
+ unsigned int pref_window:1; /* Bridge has pref mem window */
+ unsigned int pref_64_window:1; /* Pref mem window is 64-bit */
unsigned int multifunction:1; /* Multi-function device */

unsigned int is_busmaster:1; /* Is busmaster */
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