On Fri, May 31, 2013 at 4:14 PM, David Epping <david.epping@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > Hello, > > I am inspecting the MSI-X setup of some PCIe devices and have questions > about the output of lspci. > > It looks something like this: > Capabilities: [50] MSI-X: Enable+ Count=32 Masked- > Vector table: BAR=0 offset=00002000 > PBA: BAR=0 offset=00003000 > > As far as I understand the PCI 3.0 specification MSI-X capabilities define a > 32 bit register for the upper address portion of the MSI target addresses > (at capability offset 4) and another 32 bit register pointing to the BAR and > inter-BAR offset for the table of lower address portions of the MSI target > addresses (at capability offset 8). > Why are there two lines in the lspci output indicating some BAR and offset? > What do they mean? My understanding is that there are three data structures here: 1) The MSI-X Capability (Figure 6-10) in config space 2) The "MSI-X Table" (Figure 6-11) in PCI memory space 3) The "MSI-X PBA" (Pending Bit Array, Figure 6-12) in PCI memory space The "Vector table" line tells you how to find the "MSI-X Table," and the "PBA" line tells you how to find the "MSI-X PBA" table. In MSI (not MSI-X), there is only one MSI target address, and it is in the MSI capability. In MSI-X, each MSI-X vector can have its own target address, and those addresses are not in the capability itself; they are stored in the memory decoded by a BAR. In your case, you would read the bus address from BAR 0, and the vector table should be at offsets 0x2000-0x21ff (32 16-byte entries) from that address. The PBA should be at offsets 0x3000-0x30ff (32 8-byte entries). lspci will show you the BAR values, but it doesn't dump PCI memory space, so you'd have to use /dev/mem or a tool like http://cmp.felk.cvut.cz/~pisa/linux/rdwrmem.c to actually look at the tables. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
