On Mon, Feb 8, 2016 at 4:48 PM, Mark Rutland <mark.rutl...@arm.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.pa...@broadcom.com>
> > Reviewed-by: Ray Jui <r...@broadcom.com>
> > Reviewed-by: Scott Branden <sbran...@broadcom.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
)
> 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?
>
> To use features of the generic IOMMU binding, we must properly implement
> the generic IOMMU binding for the SMMU rather than bodging it onto the
> side of the existing binding.
>
> Thanks,
> Mark.
>
>
Regards,
Anup
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