On Mon, Sep 26, 2005 at 08:11:56PM -0700, Randy.Dunlap wrote:
> From: Randy Dunlap <[email protected]>
>
> MSI requires local APIC + IO APIC support (according to
> drivers/pci/Kconfig),
The purpose of MSI is to bypass the IO APIC.
I'm not aware of any dependency on IO APIC in HW.
I suspect the dependency in the Kconfig is historical
because of how the x86 source code is structured:
config X86_LOCAL_APIC
bool
depends on X86_UP_APIC || ((X86_VISWS || SMP) && !X86_VOYAGER)
default y
essentially, LOCAL_APIC gets enabled if "UP_APIC or SMP".
I've no clue why folks thought it was better to ignore
the IO APIC on UP kernels.
I'm pretty sure one only needs a local APIC support.
Local APIC responds to 0xfee00000 range of addresses and
directs the interrupt to a CPU.
> but if a kernel is built with all of
> those (APICs + CONFIG_PCI_MSI) and then booted with "nosmp" or
> "max_cpus=0|1" or "noapic" or "nolapic", MSI also should be
> disabled, otherwise the interrupt routing is bad (so that only
> using "irqpoll" helps).
UP vs SMP is orthogonal to MSI support wrt HW.
I suppose this is another historical artifact of
APICs being used with SMP x86 boxes first.
thanks,
grant
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
| |
 |