On Tue, Nov 17, 2020 at 02:47:54PM +0100, Thierry Reding wrote: > On Mon, Nov 16, 2020 at 11:48:39AM -0800, John Stultz wrote: > > On Mon, Nov 16, 2020 at 8:36 AM Will Deacon <will@xxxxxxxxxx> wrote: > > > On Mon, Nov 16, 2020 at 04:59:36PM +0100, Thierry Reding wrote: > > > > On Fri, Nov 06, 2020 at 04:27:10AM +0000, John Stultz wrote: > > > > Unfortunately, the ARM SMMU module will eventually end up being loaded > > > > once the root filesystem has been mounted (for example via SDHCI or > > > > Ethernet, both with using just plain, non-IOMMU-backed DMA API) and then > > > > initialize, configuring as "fault by default", which then results from a > > > > slew of SMMU faults from all the devices that have previously configured > > > > themselves without IOMMU support. > > > > > > I wonder if fw_devlink=on would help here? > > > > > > But either way, I'd be more inclined to revert this change if it's causing > > > problems for !QCOM devices. > > > > > > Linus -- please can you drop this one (patch 3/3) for now, given that it's > > > causing problems? > > > > Agreed. Apologies again for the trouble. > > > > I do feel like the probe timeout to handle optional links is causing a > > lot of the trouble here. I expect fw_devlink would solve this, but it > > may be awhile before it can be always enabled. I may see about > > pushing the default probe timeout value to be a little further out > > than init (I backed away from my last attempt as I didn't want to > > cause long (30 second) delays for cases like NFS root, but maybe 2-5 > > seconds would be enough to make things work better for everyone). > > I think there are two problems here: 1) the deferred probe timeout can > cause a mismatch between what SMMU masters and the SMMU think is going > on and 2) a logistical problem of dealing with the SMMU driver being a > loadable module. > > The second problem can be dealt with by shipping the module in the > initial ramdisk. That's a bit annoying, but perhaps the right thing to > do. At least on Tegra we need this because all the devices that carry > the root filesystem (Ethernet for NFS and SDHCI/USB/SATA/PCI for disk > boot) are SMMU masters and will start to fault once the SMMU driver is > loaded. Realistically, if you're building an IOMMU driver as a module then it needs to be part of the initrd and fw_devlink needs to be enabled. Relying on timeouts and the phase of the moon is not going to be reliable. But back to the original issue, I think we should revert the Kconfig patch from Linus' tree. Please can you send a revert for that? Will
