On Wed, Jan 11, 2017 at 03:59:30PM -0500, Rob Clark wrote: > On Wed, Jan 11, 2017 at 4:36 AM, Will Deacon <will.deacon@xxxxxxx> wrote: > > On Tue, Jan 10, 2017 at 02:20:13PM -0500, Rob Clark wrote: > >> On Tue, Jan 10, 2017 at 12:52 PM, Will Deacon <will.deacon@xxxxxxx> wrote: > >> > On Fri, Jan 06, 2017 at 11:26:49AM -0500, Rob Clark wrote: > >> >> Hmm, well we install the fault handler on the iommu_domain.. perhaps > >> >> maybe a combo of dts property (or deciding based on more specific > >> >> compat string), plus extra param passed in to > >> >> iommu_set_fault_hander(). The dts property or compat string to > >> >> indicate whether the iommu (and how it is wired up) can handle stalls, > >> >> and enable_stall param when fault handler is registered to indicate > >> >> whether the device itself can cope.. if either can't do stalling, then > >> >> don't set CFCFG. > >> > > >> > I thought about this some more, and I think you're right. Having > >> > iommu_set_fault_handler take a flags parameter indicating that, for example, > >> > the fault handler can deal with paging, is all we need to implement the > >> > per-master opt-in functionality for stalling faults. There's no real > >> > requirement to standardise a generic firmware property for that (but > >> > we still need *something* that says stalling is usable on the SMMU -- > >> > perhaps just the compatible string is ok). > >> > >> btw, it occurred to me that maybe it should be flags param to > >> iommu_attach_device() (just in case fault handler not installed?) > >> otoh stalling without a fault handler is silly, but I guess we need it > >> to infer whether stalling can be supported by other devices on same > >> iommu.. tbh I'm on a bit shaky ground when it comes to multiple > >> devices per iommu since the SoC's I'm familiar with do it the other > >> way around. But I guess you have thought more about the multi-device > >> case, so figured I should suggest it.. > > > > I don't think it works at attach time, because the stalling property belongs > > to the domain, rather than the individual devices within it. Similarly, I > > don't think we should allow this property to be toggled once devices have > > been attached. > > > > hmm, I was more thinking of cases where drivers for particular devices > need some work (ie. like potentially disabling hw hang detect during > faults).. I guess we could have three levels, that all have to be true > in order to enable stall: smmu, domain (pass flags in to > iommu_domain_alloc()??), and device (iommu_attach_device())? Hooking iommu_set_fault_handler, as you originally suggested, is the best way to set the flag on the domain. I think we just need to enforce that iommu_set_fault_handler is called prior to attaching devices to a domain, so that the IOMMU driver can configure the domain appropriately on the first attach. Will -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
