[LAU] HW upgrade - new computer

Clemens Ladisch clemens at ladisch.de
Thu May 1 07:52:50 UTC 2014

Len Ovens wrote:
> On Wed, 30 Apr 2014, Clemens Ladisch wrote:
>> Len Ovens wrote:
>>> PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #3 (rev d5)
>>> 00:1c.3 PCI bridge: Intel Corporation 82801 PCI Bridge (rev d5)
>>> I am not sure which is which. The first may be the express port.
>> The ASM1083 (which the manual says you have) should be listed as "ASM1083".
>> What is the output of "lspci -t"?
> len at music:~$ lspci -t
> -[0000:00]-+-00.0
>            +-01.0-[01]--
>            +-02.0
>            +-14.0
>            +-16.0
>            +-1a.0
>            +-1c.0-[02]--
>            +-1c.2-[03]----00.0
>            +-1c.3-[04-05]----00.0-[05]--+-00.0
>            |                            \-02.0
>            +-1d.0
>            +-1f.0
>            +-1f.2
>            \-1f.3
> 00:1c.3 would be the PCI bridge then as my two audio cards are listed
> as 05:00.0 and 05:02.0. I would guess that the third PCI slot would be
> 01. I see that the bridge is listed as [04-05] I am guessing that
> means 04 is the PCIe side and 05 is the PCI side?

Device 00:1c.3 is one of the PCIe ports of the southbridge.
Device 04:00 is the ASM1083 PCIe/PCI bridge.
Devices 05:xx are the chips on the PCI cards.

Bus 00: is the "root complex", i.e., CPU/northbridge/southbridge.
Bus 04: is the PCIe connection between the southbridge and the ASM1083.
Bus 05: is the PCI bus.

"[04-05]" means that both buses are reachable through this bridge.

> So it sounds like you are saying that the PCIe devices are assigned
> an irq to be compatible with the PCI standard, but most PCIe devices
> don't use the irq having another way to get the OS attention.

There are different kinds of interrupts.  0-15 are ISA-compatible
interrupts; the next four or eight can be used for PCI interrupts.
(The interrupt controller (IOAPIC) has only a limited number of
interrupt lines.)

Message-signaled interrupts (MSIs) are implemented with a different
mechanism and do not need to go through the IOAPIC; you can have any
number of them, and they are never shared between devices.

> Looking at /proc/interrupts, I see that ahci (which from lspci seems
> to be the SATA controller) shows irq 42 even though the book says it
> is sharing an irq with PCI slot 1 which has an ens1370 at irq 19. So
> I would guess that this irq 42 is a "soft" irq?

Yes, it's an MSI.

> (and why do I have an ISA bridge?)

Because you have ISA devices.  (Intel likes to call them "legacy", but
they are still there.)

> I would guess that if I installed a PCIe card that was PCI HW with
> a PCIe->PCI bridge on the card to update it, that it would still use
> the old irq and could clash with one of my other PCI audio cards.



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