Hi Sricharan, On Tuesday 16 May 2017 07:53:57 sricharan@xxxxxxxxxxxxxx wrote: > On 2017-05-16 03:04, Laurent Pinchart wrote: > > On Monday 15 May 2017 23:37:16 Laurent Pinchart wrote: > >> On Wednesday 03 May 2017 15:54:59 Sricharan R wrote: > >>> On 5/3/2017 3:24 PM, Robin Murphy wrote: > >>>> On 02/05/17 19:35, Geert Uytterhoeven wrote: > >>>>> On Fri, Feb 3, 2017 at 4:48 PM, Sricharan R wrote: > >>>>>> From: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > >>>>>> > >>>>>> Failures to look up an IOMMU when parsing the DT iommus property > >>>>>> need to be handled separately from the .of_xlate() failures to > >>>>>> support deferred probing. > >>>>>> > >>>>>> The lack of a registered IOMMU can be caused by the lack of a driver > >>>>>> for the IOMMU, the IOMMU device probe not having been performed yet, > >>>>>> having been deferred, or having failed. > >>>>>> > >>>>>> The first case occurs when the device tree describes the bus master > >>>>>> and IOMMU topology correctly but no device driver exists for the > >>>>>> IOMMU yet or the device driver has not been compiled in. Return NULL, > >>>>>> the caller will configure the device without an IOMMU. > >>>>>> > >>>>>> The second and third cases are handled by deferring the probe of the > >>>>>> bus master device which will eventually get reprobed after the > >>>>>> IOMMU. > >>>>>> > >>>>>> The last case is currently handled by deferring the probe of the bus > >>>>>> master device as well. A mechanism to either configure the bus > >>>>>> master device without an IOMMU or to fail the bus master device probe > >>>>>> depending on whether the IOMMU is optional or mandatory would be a > >>>>>> good enhancement. > >>>>>> > >>>>>> Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > >>>>>> Signed-off-by: Laurent Pichart > >>>>>> <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > >>>>>> Signed-off-by: Sricharan R <sricharan@xxxxxxxxxxxxxx> > >>>>> > >>>>> This patch broke Renesas R-Car Gen3 platforms in renesas-drivers. > >>>>> As the IOMMU nodes in DT are not yet enabled, all devices having > >>>>> iommus properties in DT now fail to probe. > >>>> > >>>> How exactly do they fail to probe? Per d7b0558230e4, if there are no > >>>> ops registered then they should merely defer until we reach the point > >>>> of giving up and ignoring the IOMMU. Is it just that you have no other > >>>> late-probing drivers or post-init module loads to kick the deferred > >>>> queue after that point? I did try to find a way to explicitly kick it > >>>> from a suitably late initcall, but there didn't seem to be any obvious > >>>> public interface - anyone have any suggestions? > >>>> > >>>> I think that's more of a general problem with the probe deferral > >>>> mechanism itself (I've seen the same thing happen with some of the > >>>> CoreSight stuff on Juno due to the number of inter-component > >>>> dependencies) rather than any specific fault of this series. > >>> > >>> I was thinking of an additional check like below to avoid the > >>> situation ? > >>> > >>> From 499b6e662f60f23740b8880882b0a16f16434501 Mon Sep 17 00:00:00 2001 > >>> From: Sricharan R <sricharan@xxxxxxxxxxxxxx> > >>> Date: Wed, 3 May 2017 13:16:59 +0530 > >>> Subject: [PATCH] iommu: of: Fix check for returning EPROBE_DEFER > >>> > >>> While returning EPROBE_DEFER for iommu masters > >>> take in to account of iommu nodes that could be > >>> marked in DT as 'status=disabled', in which case > >>> simply return NULL and let the master's probe > >>> continue rather than deferring. > >>> > >>> Signed-off-by: Sricharan R <sricharan@xxxxxxxxxxxxxx> > >>> --- > >>> > >>> drivers/iommu/of_iommu.c | 1 + > >>> 1 file changed, 1 insertion(+) > >>> > >>> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c > >>> index 9f44ee8..e6e9bec 100644 > >>> --- a/drivers/iommu/of_iommu.c > >>> +++ b/drivers/iommu/of_iommu.c > >>> @@ -118,6 +118,7 @@ static bool of_iommu_driver_present(struct > >>> device_node *np) > >>> > >>> ops = iommu_ops_from_fwnode(fwnode); > >>> if ((ops && !ops->of_xlate) || > >>> + !of_device_is_available(iommu_spec->np) || > >>> (!ops && !of_iommu_driver_present(iommu_spec->np))) > >>> return NULL; > >> > >> This looks good to me, but won't be enough. The ipmmu-vmsa driver in > >> v4.12-rc1 doesn't call iommu_device_register() and thus won't be found > >> by iommu_ops_from_fwnode(). Furthermore, it doesn't IOMMU_OF_DECLARE(), > >> and thus will always be considered as absent. > >> > >> I agree that the ipmmu-vmsa driver needs to be fixed, but it would > >> have been nice to check existing IOMMU drivers before merging this patch > >> series... > > > > Please pardon the question, but has this patch series been tested on > > ARM32 ? > > > > When the device is probed the arch_setup_dma_ops() function is called. > > It sets the device's dma_ops and the mapping (in > > __arm_iommu_attach_device()). If probe is deferred, > > arch_teardown_dma_ops() is called which in turn calls > > arch_teardown_dma_ops(). This removes the mapping but doesn't touch the > > dma_ops. The next time the device is probed, arch_setup_dma_ops() bails > > out immediately as the dma_ops are already set, leaving us with a device > > bound to IOMMU operations but with no mapping. This oopses later as soon > > as the kernel tries to map memory for the device through the IOMMU. > > Resetting the dma_ops for arm32 was added in this patch [1], which I > missed to send in the original series, but now have added to Russell's patch > tracking system. Thank you. I fear that won't be enough though. > [1] https://patchwork.kernel.org/patch/9434105/ Quoting the patch: > arch_teardown_dma_ops() being the inverse of arch_setup_dma_ops() > ,dma_ops should be cleared in the teardown path. Otherwise > this causes problem when the probe of device is retried after > being deferred. The device's iommu structures are cleared > after EPROBEDEFER error, but on the next try dma_ops will still > be set to old value, which is not right. > > Signed-off-by: Sricharan R <sricharan@xxxxxxxxxxxxxx> > Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx> > --- > arch/arm/mm/dma-mapping.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c > index ab4f745..a40f03e 100644 > --- a/arch/arm/mm/dma-mapping.c > +++ b/arch/arm/mm/dma-mapping.c > @@ -2358,6 +2358,7 @@ static void arm_teardown_iommu_dma_ops(struct device *dev) > __arm_iommu_detach_device(dev); > arm_iommu_release_mapping(mapping); > + set_dma_ops(dev, NULL); > } > #else The subject mentions arch_teardown_dma_ops(), which I think is correct, but the patch adds the set_dma_ops() call to arm_teardown_iommu_dma_ops(). However, the situation is perhaps more complex. Note the check at the beginning of arch_setup_dma_ops(): /* * Don't override the dma_ops if they have already been set. Ideally * this should be the only location where dma_ops are set, remove this * check when all other callers of set_dma_ops will have disappeared. */ if (dev->dma_ops) return; If you set the dma_ops to NULL in arm_teardown_iommu_dma_ops() or arch_teardown_dma_ops(), the next call to arch_setup_dma_ops() will override them. To be safe you should only set them to NULL if they have been set by arch_setup_dma_ops(). More than that, arch_teardown_dma_ops() should probably not call arm_teardown_iommu_dma_ops() at all if the dma_ops were set by arm_iommu_attach_device() and not arch_teardown_dma_ops(). One option would be to add a field to struct dev_archdata to store that information. To avoid growing the structure, which is embedded in every struct device, you could possibly turn the dma_coherent bool into a bitfield. @@ -19,7 +19,8 @@ struct dev_archdata { #ifdef CONFIG_XEN const struct dma_map_ops *dev_dma_ops; #endif - bool dma_coherent; + bool dma_coherent:1; + bool dma_ops_setup:1; }; struct omap_device; I haven't checked, however, whether the dma_coherent field would need to be accessed atomically, so this might be a bad idea. Last but not least, a fix must be merged in v4.12, and the sooner the better. > > I might be missing something obvious, but I don't see how this can > > work. > > > >>>>> This can be fixed by either: > >>>>> - Disabling CONFIG_IPMMU_VMSA, or > >>>>> - Reverting commit 7b07cbefb68d486f (but keeping "int ret = 0;"). > >>>>> > >>>>> Note that this was a bit hard to investigate, as R-Car Gen3 support > >>>>> wasn't upstreamed yet, so bisection pointed to a merge commit. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
