On 18 May 2017 at 16:47, Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> wrote: > On Thu, May 18, 2017 at 04:10:28PM +0100, Ard Biesheuvel wrote: > > [...] > >> >> Re _DSM: I think it makes sense to honour it, because it puts the >> >> allocation under the control of the firmware, which completely removes >> >> the burden of having to reason about a policy in the kernel. That >> >> leaves the question which will be the default, but that is of minor >> >> importance IMO. >> > >> > I agree; we should try to follow the spec unless we have a good reason >> > not to, which argues for honoring the _DSM, so I think it's worth a >> > try. Booting with "pci=realloc" could override the _DSM and taint the >> > kernel (because we don't know the effect of reassigning something the >> > firmware told us not to touch). >> > >> >> I'd like to hear Lorenzo's view on this first, but I can certainly >> respin my _DSM patch to take pci=realloc into account, and move the >> handling to generic code as well. > > I agree with both of you on _DSM implementation and interpretation. > > Now, if we use it correctly (ie by the FW standard) on ARM64 systems we > are going to trigger regressions, that's certain (ie we can then boot > with pci=realloc - still, we are breaking systems), that's the reason > why for patch(2) I'd like to create a branch and send a CFT for ARM64 > ACPI testing before queuing it (either I can set-up a testing branch > or we ask Bjorn to do it - as you guys prefer - as long as we have > a branch for people to test patch(2) on ARM64 ACPI systems). > > You still need to assign resources that could not be claimed though > so patch(2) still needs updating: > > PCI FW spec 3.1 - 4.6.5 > > "...However, the operating system is free to configure the devices in this > hierarchy that have not been configured by the firmware." > > Which in kernel-speak it means that you have to assign resources that > could not be claimed. > Right. AFAICT this is the part that is typically handled by pcibios_resource_survey() et al, whose default __weak implementations are empty functions. Shall I override those for arm64 to host this logic?
