From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Sricharan R <sricharan@codeaurora.org>
Cc: Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Magnus Damm <magnus.damm@gmail.com>,
"linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
Joerg Roedel <joro@8bytes.org>, Will Deacon <will.deacon@arm.com>,
okaya@codeaurora.org,
ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
iommu@lists.linux-foundation.org,
Geert Uytterhoeven <geert@linux-m68k.org>,
Hanjun Guo <hanjun.guo@linaro.org>,
linux-pci <linux-pci@vger.kernel.org>,
Bjorn Helgaas <bhelgaas@google.com>,
tn@semihalf.com, Robin Murphy <robin.murphy@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [PATCH V8 07/11] iommu: of: Handle IOMMU lookup failure with deferred probing or error
Date: Tue, 16 May 2017 00:34:18 +0300 [thread overview]
Message-ID: <1804176.uxVOFWagsb@avalon> (raw)
In-Reply-To: <1900421.tkAiezvoW8@avalon>
Hi Sricharan,
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@ideasonboard.com>
> >>>>
> >>>> 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@samsung.com>
> >>>> Signed-off-by: Laurent Pichart
> >>>> <laurent.pinchart+renesas@ideasonboard.com>
> >>>> Signed-off-by: Sricharan R <sricharan@codeaurora.org>
> >>>
> >>> 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@codeaurora.org>
> > 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@codeaurora.org>
> > ---
> >
> > 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.
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
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next prev parent reply other threads:[~2017-05-15 21:34 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-03 15:48 [PATCH V8 00/11] IOMMU probe deferral support Sricharan R
2017-02-03 15:48 ` [PATCH V8 01/11] iommu/of: Refactor of_iommu_configure() for error handling Sricharan R
2017-03-08 18:58 ` Jean-Philippe Brucker
2017-03-08 19:28 ` Robin Murphy
2017-03-09 9:52 ` sricharan
2017-03-09 11:21 ` Robin Murphy
2017-02-03 15:48 ` [PATCH V8 02/11] iommu/of: Prepare for deferred IOMMU configuration Sricharan R
2017-02-03 15:48 ` [PATCH V8 03/11] of: dma: Move range size workaround to of_dma_get_range() Sricharan R
2017-02-03 15:48 ` [PATCH V8 04/11] of: dma: Make of_dma_deconfigure() public Sricharan R
2017-02-03 15:48 ` [PATCH V8 05/11] ACPI/IORT: Add function to check SMMUs drivers presence Sricharan R
2017-02-03 15:48 ` [PATCH V8 06/11] of/acpi: Configure dma operations at probe time for platform/amba/pci bus devices Sricharan R
2017-02-03 15:48 ` [PATCH V8 07/11] iommu: of: Handle IOMMU lookup failure with deferred probing or error Sricharan R
2017-05-02 18:35 ` Geert Uytterhoeven
2017-05-03 9:54 ` Robin Murphy
2017-05-03 10:24 ` Sricharan R
2017-05-03 11:13 ` Sricharan R
2017-05-05 13:23 ` Geert Uytterhoeven
2017-05-17 9:22 ` Magnus Damm
2017-05-17 10:28 ` Sricharan R
2017-05-15 14:22 ` Will Deacon
2017-05-16 2:26 ` sricharan
2017-05-15 20:37 ` Laurent Pinchart
2017-05-15 21:34 ` Laurent Pinchart [this message]
2017-05-16 2:23 ` sricharan
2017-05-16 7:17 ` Laurent Pinchart
2017-05-16 9:47 ` Sakari Ailus
2017-05-16 13:40 ` sricharan
2017-05-16 14:06 ` Laurent Pinchart
2017-05-16 14:04 ` Robin Murphy
2017-05-16 14:10 ` Laurent Pinchart
2017-05-16 14:29 ` sricharan
2017-05-16 14:46 ` Laurent Pinchart
2017-05-16 14:52 ` Robin Murphy
2017-02-03 15:48 ` [PATCH V8 08/11] drivers: acpi: " Sricharan R
2017-02-03 16:15 ` Sricharan
2017-02-03 17:39 ` Robin Murphy
2017-02-05 6:51 ` Sricharan
2017-02-03 15:48 ` [PATCH V8 09/11] arm64: dma-mapping: Remove the notifier trick to handle early setting of dma_ops Sricharan R
2017-02-03 15:48 ` [PATCH V8 10/11] iommu/arm-smmu: Clean up early-probing workarounds Sricharan R
2017-02-03 15:48 ` [PATCH V8 11/11] ACPI/IORT: Remove linker section for IORT entries probing Sricharan R
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