From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC/PATCH 8/9] iommu: of: Handle IOMMU lookup failure with deferred probing or error
Date: Thu, 28 May 2015 14:31:09 +0100 [thread overview]
Message-ID: <20150528133109.GJ31001@arm.com> (raw)
In-Reply-To: <1431644410-2997-9-git-send-email-laurent.pinchart+renesas@ideasonboard.com>
Hi Laurent,
On Fri, May 15, 2015 at 12:00:09AM +0100, Laurent Pinchart wrote:
> 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.
I appreciate that you're just looking to handle early initialisation
failures here, but do you have any thoughts on how to deal with failures
later on when e.g. the DMA-mapping API is trying to create IOMMU domains.
One potential problem I foresee is if we try to add all devices to a common
DMA domain, we may get -ENOSPC-style failures due to limited resources on
the IOMMU. In this case, we'd probably want to fall-back to non-IOMMU DMA
ops, but that in-turn could have consequences on things like dma-coherent.
It's all a bit murky, so I'd be glad to hear any thoughts you might have
around this.
Anyway, this patch looks fine:
Acked-by: Will Deacon <will.deacon@arm•com>
but we should consider how all of this will get used too.
Will
next prev parent reply other threads:[~2015-05-28 13:31 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-14 23:00 [RFC/PATCH 0/9] IOMMU probe deferral support Laurent Pinchart
2015-05-14 23:00 ` [RFC/PATCH 1/9] arm: dma-mapping: Don't override dma_ops in arch_setup_dma_ops() Laurent Pinchart
2015-05-27 17:38 ` Will Deacon
2015-05-14 23:00 ` [RFC/PATCH 2/9] arm: dma-mapping: Support IOMMU mappings spanning the full 32 bits range Laurent Pinchart
2015-05-19 10:17 ` Robin Murphy
2015-05-24 22:38 ` Laurent Pinchart
2015-05-14 23:00 ` [RFC/PATCH 3/9] of: dma: Move range size workaround to of_dma_get_range() Laurent Pinchart
2015-05-27 17:59 ` Will Deacon
2015-05-28 2:37 ` Rob Herring
2015-05-14 23:00 ` [RFC/PATCH 4/9] of: dma: Make of_dma_deconfigure() public Laurent Pinchart
2015-05-28 12:42 ` Will Deacon
2015-05-29 14:04 ` Rob Herring
2015-05-14 23:00 ` [RFC/PATCH 5/9] of: dma: Split of_configure_dma() into mask and ops configuration Laurent Pinchart
2015-05-28 13:01 ` Will Deacon
2015-05-29 14:19 ` Rob Herring
2015-05-14 23:00 ` [RFC/PATCH 6/9] drivers: platform: Configure dma operations at probe time Laurent Pinchart
2015-05-15 23:59 ` Greg Kroah-Hartman
2015-05-19 10:39 ` Robin Murphy
2015-05-24 22:41 ` Laurent Pinchart
2015-05-14 23:00 ` [RFC/PATCH 7/9] iommu: of: Document the of_iommu_configure() function Laurent Pinchart
2015-05-28 13:02 ` Will Deacon
2015-05-14 23:00 ` [RFC/PATCH 8/9] iommu: of: Handle IOMMU lookup failure with deferred probing or error Laurent Pinchart
2015-05-28 13:31 ` Will Deacon [this message]
2015-05-14 23:00 ` [RFC/PATCH 9/9] iommu/ipmmu-vmsa: Use DT-based instantiation Laurent Pinchart
2015-05-27 13:26 ` [RFC/PATCH 0/9] IOMMU probe deferral support Marek Szyprowski
2015-05-28 17:36 ` Laura Abbott
2015-06-11 16:25 ` Will Deacon
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