On 02/02/17 11:26, Will Deacon wrote: > On Wed, Feb 01, 2017 at 09:19:22PM +0200, Michael S. Tsirkin wrote: >> On Wed, Feb 01, 2017 at 06:27:09PM +0000, Will Deacon wrote: >>> On Wed, Feb 01, 2017 at 08:09:21PM +0200, Michael S. Tsirkin wrote: >>>> I'd like to do that instead. It's fastboot doing the unreasonable thing >>>> here and deviating from what every other legacy device without exception >>>> did for years. If this means fastboot will need to update to virtio 1, >>>> all the better. >>> >>> The problem still exists with virtio 1, unless we require that the >>> "dma-coherent" property is set/unset correctly when VIRTIO_F_IOMMU_PLATFORM >>> is advertised by the device (which is what I suggested in my reply). >> >> I'm not ignoring that, but I need to understand that part a bit better. >> I'll reply to that patch in a day or two after looking at how _CCA is >> supposed to work. > > Thanks. I do think that whatever solution we come up with for virtio 1 > should influence what we do for legacy. > >>> We can't detect the fastmodel, >> >> Surely, it puts a hardware id somewhere? I think you mean >> fastmodel isn't always affected, right? > > I don't think there's a hardware ID. The thing is, the fastmodel is a > toolkit for building all sorts of platforms: you can chop and change > the CPUs, the peripherals, the memory, the interrupt controller, the > interconnect etc. Pretty much everything can be customised. So, for > any fastmodel configuration that places virtio upstream of the SMMU > (which is common, because virtio is one of the few DMA-capable peripherals > that the fastmodel supports), we need to do something special. > >> I'd like to see basically >> >> if (fastmodel) >> a pile of special work-arounds >> else >> not less hacky but more common virtio work-arounds >> >> :) >> >> And then I can apply whatever comes from @arm.com and not >> worry about breaking actual hardware. > > What we could do is call iommu_group_get(&vdev->dev) for legacy Actually, that should be vdev->dev.parent - I'm now not sure quite what I managed to successfully test yesterday, but apparently it wasn't this patch :( > devices if CONFIG_ARM64. If that returns non-NULL, then we know that > the device is upstream of an SMMU, which means it must be the fastmodel. We can boot 32-bit kernels on models, so I'd be inclined to keep CONFIG_ARM included, but I do tend to agree that explicitly checking for an IOMMU is probably the cleanest approach if we reposition this as a more specific quirk. I'll split apart the "Fast Models are wacky" vs. "uh-oh device coherency" aspects and spin a v2 so that we can (hopefully) sort the regression out ASAP. Robin. > > 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
