Thierry Reding <thierry.reding@xxxxxxxxx> wrote @ Fri, 1 Nov 2013 10:46:45 +0100: > * PGP Signed by an unknown key > > On Thu, Oct 31, 2013 at 11:53:22AM -0600, Stephen Warren wrote: > > On 10/31/2013 10:46 AM, Hiroshi Doyu wrote: > > > Stephen Warren <swarren@xxxxxxxxxxxxx> wrote @ Thu, 31 Oct 2013 17:35:24 +0100: > > > > > > ... > > >>>> ... and for the driver to explicitly parse that property, and wait > > >>>> until the driver for iommu_phandle is ready. Exactly the same as any > > >>>> other resource/service dependency. > > >>>> > > >>>> That will solve all the problems. > > >>>> > > >>>> The only downside is that every driver needs to contain code to parse > > >>>> that property. However, I think that's just one function call; the > > >>>> actual implementation of that function can be unified somewhere inside > > >>>> core code in drivers/iommu/. > > >>> > > >>> Yes, but only missing part now is that, we could do this with > > >>> "bus_notifier", but the current bus_notifier doesn't have the feature > > >>> to return error(-EPROBE_DEFER). This could be modified so that > > >>> bus_notifier could return (-EPROBE_DEFER) to postpone > > >>> probing. Alternatively this could be done in some core probe code as > > >>> well as Thierry pointed out. > > >>> > > >>> [1] In the reply of "[PATCHv3 14/19] iommu/tegra: smmu: Get "nvidia,memory-clients" from DT" > > >> > > >> I think this should be done explicitly in drivers. It's much > > >> simpler, > > > > > > Yes, we need to insert some IOMMU specific code in driver? > > > > > >> and doesn't encode any knowledge of driver-specific bindings into some > > >> common bus notifier code. > > > > > > I think that we cannot do that in drivers. We want to use drivers as > > > they are without any modifications indicating its dependency on > > > IOMMU because most of drivers are existing ones which nvidia doesn't > > > implement. We want to set up any IOMMU related thingy implicitly, > > > hided from driver. That's why we need to do this in bus_notifier or > > > driver core code. > > > > We're talking about memory-mapped on-SoC devices here, that generally > > only exist inside Tegra SoCs. > > > > Even ignoring that (i.e. expanding the argument to arbitrary modules), > > having drivers that perform bus-master transactions call a function > > of_iommu_attach() or similar, which does nothing if the device isn't > > behind an IOMMU but otherwise does whatever is required, seems like it > > isn't much of an imposition. > > > > If this turns out to be something that lots of devices benefit from, we > > could do the same thing that pinctrl does for "hogs", and make the > > function call in the driver core. But note that's still part of the > > probing flow (just implemented in the driver core) rather than bus > > notifier based, hence keeps the same simplicity. > > That's exactly what I was proposing in the first place. I did the same > thing in my patches for late interrupt reference resolution. The reason > why I think it makes sense to put it into the core is that it's > something that likely most devices will have to do anyway. And it also > is completely transparent to drivers, right? If they aren't attached to > an IOMMU then they just aren't but will continue to work properly. And > as you said, having it in the core makes drivers simpler, while at the > same time keeping the explicitness of having a function call (rather > than a somewhat obfuscated bus notifier) and the flexibility of deferred > probing. One idea is that, rather than inserting a hook(function) per subsystems in driver core, if we invent a new /special section/ which collects all hooks in sequence like initcalls, the subsystem just would declare a hook function for that special section. All hooks in that section can be called from driver core iterately. Then we wouldn't touch driver core code at all, once we insert a func to call hooks repeatedly. Looks simpler than tweaking bus notifier. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
