On Sat, 28 Jul 2012 08:29:31 -0800 Chen Tian (CT) wrote:
CT> So I should use the interrupt pin field at offset 0x3c to find out which CT> PCI link the device uses.
Yes, but the offset of the interrupt pin ix 0x3d.
CT> Can I use this value directly to search IO-APIC CT> GSI in _PRT blocks? I read some article that says this value may be local CT> to PCI device, and it may be remapped by motherboard to another PCI link CT> number through something like daisy chain type of mapping. For example, PCI CT> slot 1's INTA# uses INTA#, while PCI slot 2's INTA# actually uses INTB#. CT> Is this true? If so, I think I need to handle this mapping before search CT> _PRT blocks, right?
The _PRT method is defined in the ACPI specification as follows:
Field Type Description Address DWORD The address of the device (uses the same format as _ADR). Pin BYTE The PCI pin number of the device (0INTA, 1INTB, 2INTC, 3INTD). Source NamePath Name of the device that allocates the interrupt to which the above pin is Or connected. The name can be a fully qualified path, a relative path, or a simple BYTE name segment that utilizes the namespace search rules. Note: This field is a NamePath and not a String literal, meaning that it should not be surrounded by quotes. If this field is the integer constant Zero (or a BYTE value of 0), then the interrupt is allocated from the global interrupt pool. Source DWORD Index that indicates which resource descriptor in the resource template of the Index device pointed to in the Source field this interrupt is allocated from. If the Source field is the BYTE value zero, then this field is the global system interrupt number to which the pin is connected.
Once you've found the PCI device in the ACPI namespace, you need to look at the "Source" field to see which upstream device a PCI pin is connected to and "Source Index" tells you where it is connected. You then need to do the same for the upstream device, and so forth. For example, you may find that INTA is connected to INTC upstream, and INTC is connected to INTB even further upstream. Once you find that the "Source" field is 0, the "Source Index" is the GSI number that you are looking for.
CT> For GSI number, I assume it is the irq number I am looking for. But I still CT> have some questions. First, is it always fixed for each pin of each CT> IO-APIC? For example, first pin of first IO-APIC has GSI 0, second pin has CT> 1, ..., and the first pin of second IO-APIC has GSI 24, second pin has 25, CT> ...? If so, then irq number will range from 0 to 47 on a two-io-apic CT> machine. But Linux runs on the same machine can report irq 53 for some CT> device, which is very confusing to me.
The ACPI MADT table lists all the IOAPICs in the system. Each IOAPIC has a certain number of pins, which you can read out from the IOAPIC itself. The first IOAPIC serves GSI 0 through X-1, where X is the number of pins. The second IOAPIC then serves pins X through X + (Y-1), where Y is the number of pins of the second IOAPIC and so forth.
CT> Second, some document says GSI number can be overridden. When booting CT> Fiasco.OC, I can see a line like ovr[0] 2->0. Does that mean GSI 2 CT> eventually become irq 0? I am not sure when and why a GSI number needs to CT> be overridden, but can the overriding happen to the device I am CT> interested? If so, how should I deal with it in my device driver, i.e., CT> should I use the original GSI number as my device's irq or use the one CT> after overriding?
The legacy IRQs are also connected to the IOAPIC, typically in a 1:1 fashion. This means IRQx is connected to GSIx, except where overrides are used. This is only relevant if you want to drive a non-PCI legacy device, such as the PIT, which uses IRQ0, which is typically connected to GSI2.
Cheers, Udo