On 13/03/17 17:39, Mason wrote: > On 13/03/2017 18:12, Robin Murphy wrote: > >> On 13/03/17 16:10, Mason wrote: >> >>> 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? >>> >>> Can someone provide examples of such cards, so that I may test them >>> on both revisions? >>> >>> I was told to check ath9k-based cards. Any other examples? >>> >>> Looking around, I came across this thread: >>> http://lists.infradead.org/pipermail/linux-arm-kernel/2016-March/418254.html >>> "i.MX6 PCIe: Fix imx6_pcie_deassert_core_reset() polarity" >>> >>> IIUC, although some PCIe boards do support MSI, the driver might not >>> put in the work to use that infrastructure, and instead reverts to >>> legacy interrupts. (So it is a SW issue, in a sense.) >> >> Secondary to that category is endpoints which nominally support MSI, but >> in a way which is unreliable or otherwise broken. My experience shows >> that the Silicon Image SiI 3132 (as integrated on ARM Juno boards, but >> seemingly also relatively common on 'generic' 2-port SATA cards) falls >> into that category - using the command-line parameter to force MSIs >> instead of legacy interrupts leads to the the machine barely reaching >> userspace before something goes horribly wrong: > > Do drivers typically support *both* MSI and INTx? I'm not sure about "typically", but it certainly happens. For example, the Intel e1000e NIC driver is one I know of which can fall back from MSI-X to MSI to legacy dynamically. > Specifically, would the xhci driver support both? Line 415 of xhci.c would appear to imply so. > If I remove MSI support from my kernel, I might be able to test > legacy interrupt support that way, right? Indeed, disabling CONFIG_PCI_MSI should leave drivers with no other choice. Robin. > > Regards. >
