linux-kernel - Re: [PATCH v2 4/4] iommu/arm-smmu: Add stub of_xlate() operation in SMMUv1/SMMUv2 driver

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Date:	Mon, 8 Feb 2016 13:42:26 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Anup Patel <anup.patel@...adcom.com>,
	Robin Murphy <Robin.Murphy@....com>
Cc:	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Joerg Roedel <joro@...tes.org>,
	Sricharan R <sricharan@...eaurora.org>,
	Linux IOMMU <iommu@...ts.linux-foundation.org>,
	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Device Tree <devicetree@...r.kernel.org>,
	Ray Jui <rjui@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	Vikram Prakash <vikramp@...adcom.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH v2 4/4] iommu/arm-smmu: Add stub of_xlate() operation in
 SMMUv1/SMMUv2 driver

On Mon, Feb 08, 2016 at 06:13:11PM +0530, Anup Patel wrote:
> On Mon, Feb 8, 2016 at 4:48 PM, Mark Rutland <mark.rutland@....com> wrote:
> > On Mon, Feb 08, 2016 at 10:47:32AM +0530, Anup Patel wrote:
> >> To allow use of large memory (> 4Gb) with 32bit devices we need to use
> >> IOMMU based DMA mappings for such 32bit devices. The IOMMU dt-bindings
> >> allows us do this by specifying 'iommus' attribute in 32bit device DT
> >> node. Unfortunately, specifying 'iommus' attribute does not work with
> >> current SMMUv1/SMMUv2 driver because it requires of_xlate() operation
> >> to be implemented by the driver.
> >>
> >> This patch adds a stub implementation of of_xlate() in SMMUv1/SMMUv2
> >> driver to allow usage of 'iommus' attribute in DT for 32bit devices.
> >>
> >> Signed-off-by: Anup Patel <anup.patel@...adcom.com>
> >> Reviewed-by: Ray Jui <rjui@...adcom.com>
> >> Reviewed-by: Scott Branden <sbranden@...adcom.com>
> >> ---
> >>  drivers/iommu/arm-smmu.c | 11 +++++++++++
> >>  1 file changed, 11 insertions(+)
> >>
> >> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> >> index 02cd67d..8e090d8 100644
> >> --- a/drivers/iommu/arm-smmu.c
> >> +++ b/drivers/iommu/arm-smmu.c
> >> @@ -1398,6 +1398,16 @@ static int arm_smmu_init_platform_device(struct device *dev,
> >>       return 0;
> >>  }
> >>
> >> +int arm_smmu_of_xlate(struct device *dev, struct of_phandle_args *args)
> >> +{
> >> +     /*
> >> +      * Nothing to do here because SMMU is already aware of all
> >> +      * MMU masters and their stream IDs using mmu-master attibute
> >> +      * SMMU DT node.
> >> +      */
> >> +     return 0;
> >> +}
> >
> > NAK to this.
> 
> I had no intention in continuing this change if I knew some work
> on generic IOMMU binding was in-progress. In fact, I had asked
> about alternate options previously. (Refer,
> http://lists.infradead.org/pipermail/linux-arm-kernel/2016-January/403128.html)

Ok.

To be clear, I expect the generic binding alone to be used for the case
you described, regardless of who implements that or how long it takes to
appear.

> > As previously mentioned by others [1], this is an abuse of the generic
> > iommu binding support code.
> >
> > The SMMU binding currently does not define its implementation of the
> > generic IOMMU binding. This series did not define what an SMMU's
> > #iommu-cells would be nor what the contained values would represent.
> > Therefore it is not valid to use an SMMU node with an iommus property as
> > the SMMu doesn't follwo the generic IOMMU binding.
> >
> > There is ongoing work to have generic iommu binding support for the
> > SMMU. In the absence of documentation for what this means for the
> > binding, I am worried that this hack harms that effort.
> 
> Thanks for the info, I would like to try this on Broadcom SoCs.
> 
> Whats the ETA of patches for generic IOMMU binding for SMMU?

That I do not know.

Robin, what's the state of the generic IOMMU binding support?

Thanks,
Mark.