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Subject[patch 2.6] fix bug in pci_setup_bridge()
This bug prevents Alphas with older firmware from booting if there
is a card with PCI-PCI bridge that supports 32-bit IO.
This has happened on AS2100 with a quad-tulip card, for example:
- initially, the I/O window of 21152 bridge was 0x10000-0x10fff,
as set up by firmware;
- pci_setup_bridge() is going to change this, say, to 0xa000-0xafff:
first, it updates PCI_IO_BASE_UPPER16 and PCI_IO_LIMIT_UPPER16
registers, so that IO window temporarily is at 0x0000-0x0fff,
which effectively blocks up all legacy IO ports in the lower
4K range, such as serial, floppy, RTC an so on;
does debugging printk - machine dies here with recursive
machine checks as the serial console has gone.
Moving (or disabling) the debugging printk is not a solution -
there is possibility that timer interrupt (which might access RTC
ports) occurs between writes to lower and upper parts of the
base/limit registers.

The patch temporarily disables the IO window of the bridge by
setting PCI_IO_BASE_UPPER16 > PCI_IO_LIMIT_UPPER16 before doing
an update. It's safe, as we don't have any active IO behind
the bridge at this point. Also, it's a NOP for bridges with
16-bit-only IO.
Similar (but simpler, as we always clear upper 32 bits) fix
for 64-bit prefetchable MMIO range.
Ivan.

--- 2.6/drivers/pci/setup-bus.c Sat Oct 18 01:43:35 2003
+++ linux/drivers/pci/setup-bus.c Tue Oct 21 14:43:30 2003
@@ -132,13 +132,19 @@ pci_setup_cardbus(struct pci_bus *bus)
PCI-to-PCI Bridge Architecture Specification rev. 1.1 (1998)
requires that if there is no I/O ports or memory behind the
bridge, corresponding range must be turned off by writing base
- value greater than limit to the bridge's base/limit registers. */
+ value greater than limit to the bridge's base/limit registers.
+
+ Note: care must be taken when updating I/O base/limit registers
+ of bridges which support 32-bit I/O. This update requires two
+ config space writes, so it's quite possible that an I/O window of
+ the bridge will have some undesirable address (e.g. 0) after the
+ first write. Ditto 64-bit prefetchable MMIO. */
static void __devinit
pci_setup_bridge(struct pci_bus *bus)
{
struct pci_dev *bridge = bus->self;
struct pci_bus_region region;
- u32 l;
+ u32 l, io_upper16;

DBGC((KERN_INFO "PCI: Bus %d, bridge: %s\n",
bus->number, pci_name(bridge)));
@@ -151,20 +157,22 @@ pci_setup_bridge(struct pci_bus *bus)
l |= (region.start >> 8) & 0x00f0;
l |= region.end & 0xf000;
/* Set up upper 16 bits of I/O base/limit. */
- pci_write_config_word(bridge, PCI_IO_BASE_UPPER16,
- region.start >> 16);
- pci_write_config_word(bridge, PCI_IO_LIMIT_UPPER16,
- region.end >> 16);
+ io_upper16 = (region.end & 0xffff0000) | (region.start >> 16);
DBGC((KERN_INFO " IO window: %04lx-%04lx\n",
region.start, region.end));
}
else {
/* Clear upper 16 bits of I/O base/limit. */
- pci_write_config_dword(bridge, PCI_IO_BASE_UPPER16, 0);
+ io_upper16 = 0;
l = 0x00f0;
DBGC((KERN_INFO " IO window: disabled.\n"));
}
+ /* Temporarily disable the I/O range before updating PCI_IO_BASE. */
+ pci_write_config_dword(bridge, PCI_IO_BASE_UPPER16, 0x0000ffff);
+ /* Update lower 16 bits of I/O base/limit. */
pci_write_config_dword(bridge, PCI_IO_BASE, l);
+ /* Update upper 16 bits of I/O base/limit. */
+ pci_write_config_dword(bridge, PCI_IO_BASE_UPPER16, io_upper16);

/* Set up the top and bottom of the PCI Memory segment
for this bus. */
@@ -181,8 +189,9 @@ pci_setup_bridge(struct pci_bus *bus)
}
pci_write_config_dword(bridge, PCI_MEMORY_BASE, l);

- /* Clear out the upper 32 bits of PREF base/limit. */
- pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32, 0);
+ /* Clear out the upper 32 bits of PREF limit.
+ If PCI_PREF_BASE_UPPER32 was non-zero, this temporarily
+ disables PREF range, which is ok. */
pci_write_config_dword(bridge, PCI_PREF_LIMIT_UPPER32, 0);

/* Set up PREF base/limit. */
@@ -198,6 +207,9 @@ pci_setup_bridge(struct pci_bus *bus)
DBGC((KERN_INFO " PREFETCH window: disabled.\n"));
}
pci_write_config_dword(bridge, PCI_PREF_MEMORY_BASE, l);
+
+ /* Clear out the upper 32 bits of PREF base. */
+ pci_write_config_dword(bridge, PCI_PREF_BASE_UPPER32, 0);

/* Check if we have VGA behind the bridge.
Enable ISA in either case (FIXME!). */
-
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