From: sricharan@codeaurora.org
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: okaya@codeaurora.org,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
linux-arm-msm@vger.kernel.org, Joerg Roedel <joro@8bytes.org>,
Magnus Damm <magnus.damm@gmail.com>,
Will Deacon <will.deacon@arm.com>,
Linux-Renesas <linux-renesas-soc@vger.kernel.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-msm-owner@vger.kernel.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 19:59:01 +0530 [thread overview]
Message-ID: <4484f88d5ce342a3a27a00ef12869acc@codeaurora.org> (raw)
In-Reply-To: <1825810.fLbCv8umR7@avalon>
Hi,
On 2017-05-16 19:40, Laurent Pinchart wrote:
> Hi Robin,
>
> On Tuesday 16 May 2017 15:04:55 Robin Murphy wrote:
>> On 16/05/17 08:17, Laurent Pinchart wrote:
>> > On Tuesday 16 May 2017 07:53:57 sricharan@codeaurora.org wrote:
>
> [snip]
>
>> >> 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@codeaurora.org>
>> >> Reviewed-by: Robin Murphy <robin.murphy@arm.com>
>> >> ---
>> >>
>> >> 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().
>>
>> Under what circumstances is that an issue? We'll only be tearing down
>> the DMA ops when unbinding the driver,
>
> Or when deferring probe.
>
>> and I think it would be erroneous to expect the device to retain much
>> state
>> after that. Everything else would be set up from scratch again if it
>> get
>> reprobed later, so why not the DMA ops?
>
> Because the DMA ops might have been set elsewhere than
> arch_setup_dma_ops().
> If you look at the patch that added the above warning, its commit
> message
> states
>
> commit 26b37b946a5c2658dbc37dd5d6df40aaa9685d70 (iommu-joerg/arm/core)
> Author: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> Date: Fri May 15 02:00:02 2015 +0300
>
> arm: dma-mapping: Don't override dma_ops in arch_setup_dma_ops()
>
> The arch_setup_dma_ops() function is in charge of setting dma_ops
> with a
> call to set_dma_ops(). set_dma_ops() is also called from
>
> - highbank and mvebu bus notifiers
> - dmabounce (to be replaced with swiotlb)
> - arm_iommu_attach_device
>
> (arm_iommu_attach_device is itself called from IOMMU and bus master
> device drivers)
>
> To allow the arch_setup_dma_ops() call to be moved from device add
> time
> to device probe time we must ensure that dma_ops already setup by
> any of
> the above callers will not be overriden.
>
> Aftering replacing dmabounce with swiotlb, converting IOMMU drivers
> to
> of_xlate and taking care of highbank and mvebu, the workaround
> should be
> removed.
>
> I'm concerned about potentially breaking these if we unconditionally
> remove
> the DMA ops and mapping.
arch_teardown_dma_ops does nothing if there is
no mapping (not behind iommu), dma_ops without iommu is ok.
But when the arm_iommu_create_mapping/arm_iommu_attach_device
was called previously in the iommu driver, after we teardown,
that path in the iommu driver which called those functions is not
replayed.
Regards,
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linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2017-05-16 14:29 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
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 [this message]
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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