Hi Laurent,
On 2017-05-16 03:04, Laurent Pinchart wrote:
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@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.
[1] https://patchwork.kernel.org/patch/9434105/
Regards,
Sricharan
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.
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