[PATCH] x86: avoid wasting IRQs for PCI devices
I have submitted the patch for x86_64, this is submission for i386.
The patch changes the way IRQs are handed out to PCI devices. Currently,
each I/O APIC pin gets associated with an IRQ, no matter if the pin is used
or not. This imposes severe limitation on systems that have designs that
employ many I/O APICs, only utilizing couple lines of each, such as P64H2
chipset. It is used in ES7000, and currently, there is no way to boot the
system with more that 9 I/O APICs.
The simple change below allows to boot a system with say 64 (or more) I/O
APICs, each providing 1 slot, which otherwise impossible because of the IRQ
gaps created for unused lines on each I/O APIC. It does not resolve the
problem with number of devices that exceeds number of possible IRQs, but
eases up a tension for IRQs on any large system with potentually large
number of devices.
Signed-off-by: Natalie Protasevich <Natalie.Protasevich@unisys.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/arch/i386/kernel/mpparse.c b/arch/i386/kernel/mpparse.c
index 0a06105..383a116 100644
--- a/arch/i386/kernel/mpparse.c
+++ b/arch/i386/kernel/mpparse.c
@@ -1058,11 +1058,20 @@
}
}
+#define MAX_GSI_NUM 4096
+
int mp_register_gsi (u32 gsi, int edge_level, int active_high_low)
{
int ioapic = -1;
int ioapic_pin = 0;
int idx, bit = 0;
+ static int pci_irq = 16;
+ /*
+ * Mapping between Global System Interrups, which
+ * represent all possible interrupts, and IRQs
+ * assigned to actual devices.
+ */
+ static int gsi_to_irq[MAX_GSI_NUM];
#ifdef CONFIG_ACPI_BUS
/* Don't set up the ACPI SCI because it's already set up */
@@ -1097,11 +1106,26 @@
if ((1<<bit) & mp_ioapic_routing[ioapic].pin_programmed[idx]) {
Dprintk(KERN_DEBUG "Pin %d-%d already programmed\n",
mp_ioapic_routing[ioapic].apic_id, ioapic_pin);
- return gsi;
+ return gsi_to_irq[gsi];
}
mp_ioapic_routing[ioapic].pin_programmed[idx] |= (1<<bit);
+ if (edge_level) {
+ /*
+ * For PCI devices assign IRQs in order, avoiding gaps
+ * due to unused I/O APIC pins.
+ */
+ int irq = gsi;
+ if (gsi < MAX_GSI_NUM) {
+ gsi = pci_irq++;
+ gsi_to_irq[irq] = gsi;
+ } else {
+ printk(KERN_ERR "GSI %u is too high\n", gsi);
+ return gsi;
+ }
+ }
+
io_apic_set_pci_routing(ioapic, ioapic_pin, gsi,
edge_level == ACPI_EDGE_SENSITIVE ? 0 : 1,
active_high_low == ACPI_ACTIVE_HIGH ? 0 : 1);