On Mon, Mar 13, 2017 at 05:10:57PM +0100, Mason wrote: > Hello, > > There are two revisions of our PCI Express controller. > > Rev 1 did not support the following features: > > 1) legacy PCI interrupt delivery (INTx signals) > 2) I/O address space > > Internally, someone stated that such missing support would prevent > some PCIe cards from working with our controller. > > Are there really modern PCIe cards that require 1) and/or 2) > to function? >From a spec point of view, all endpoints, including Legacy, PCI Express, and Root Complex Integrated Endpoints, are "required to support MSI or MSI-X or both if an interrupt resource is requested" (PCIe r3.0, sec 1.3.2). The same section says Legacy Endpoints are permitted to use I/O Requests, but PCI Express and Root Complex Integrated Endpoints are not. There's a little wiggle room in the I/O BAR description; I would interpret it to mean the latter two varieties are permitted to have I/O BARs, but they must make the resources described by those BARs available via a memory BAR as well, so they can operate with I/O address space. But that's only in theory; David has already given examples of devices that don't support MSI, and Greg hinted at new devices that might require I/O space. I'm particularly curious about that last one, because there are several host bridges that don't support I/O space at all. Bjorn
