Hi Sricharan, On Wed, May 03, 2017 at 03:54:59PM +0530, 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 <sricharan@xxxxxxxxxxxxxx> 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; Without this patch, v4.12-rc1 hangs on my Juno waiting to mount the root filesystem. The problem is that the USB controller is behind an SMMU which is marked as 'status = "disabled"' in the devicetree. Whilst there was a separate thread with Ard about exactly what this means in terms of the DMA ops used by upstream devices, your patch above fixes the regression and I think should go in regardless. The DMA ops issue will likely require an additional DT binding anyway, to advertise the behaviour of the IOMMU when it is disabled. Tested-by: Will Deacon <will.deacon@xxxxxxx> Acked-by: Will Deacon <will.deacon@xxxxxxx> Could you resend it as a proper patch, please? Will -- 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
