On 20.08.2021 16:34, Julien Grall wrote: > On 20/08/2021 13:19, Rahul Singh wrote: >>> On 19 Aug 2021, at 1:31 pm, Julien Grall <jul...@xen.org> wrote: >>> On 19/08/2021 13:02, Rahul Singh wrote: >>>> Add cmdline boot option "pci=on" to enable/disable the PCI init during >>>> boot. >>> >>> I read this as "PCI" will be either disabled/enabled for the platform. >>> Whereas, I think it will be used to decide whether Xen discover PCI and PCI >>> passthrough is supported or not. >> >> Yes. I will modify the option to "pci-passthrough== <boolean>" >>> >>> Can you also clarify why a user would want to select "pci=off"? >> >> As pci-passthrough support emulate the PCI devices for DOM0 also, I thought >> if someone want to >> boot the DOM0 without emulating the PCI device in XEN and wants to have >> direct access to device. > > Dom0 will always have direct access to the PCI device. The only > difference is whether the access to the hostbridge and config space will > be trapped by Xen. I expect the both to mainly happen during boot and > therefore the overhead will be limited. > >> >> I am ok to drop this patch if you feel adding the option is not required at >> all. > One of the reason I could see this option to be useful is to figure out > if an issue occurs because of the hostbridge emulation. Yet, I am still > not fully convinced adding an option is worth it. > > Jan and others, any opinions?
Well, if there's a proper fallback, then why not allow using it in case of problems? Jan
