[RFC,6/6] iommu/arm-smmu: Update bindings document for smmu-inst-as-data DT option

This patch adds info about 'smmu-inst-as-data' DT option in ARM
SMMUv1/SMMUv2 driver bindings document.

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Vikram Prakash <vikramp@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
---
 Documentation/devicetree/bindings/iommu/arm,smmu.txt | 8 ++++++++
 1 file changed, 8 insertions(+)

On Wed, Jan 27, 2016 at 10:51:19AM +0530, Anup Patel wrote:
> This patch adds info about 'smmu-inst-as-data' DT option in ARM
> SMMUv1/SMMUv2 driver bindings document.
> 
> Signed-off-by: Anup Patel <anup.patel@broadcom.com>
> Reviewed-by: Ray Jui <rjui@broadcom.com>
> Reviewed-by: Vikram Prakash <vikramp@broadcom.com>
> Reviewed-by: Scott Branden <sbranden@broadcom.com>
> ---
>  Documentation/devicetree/bindings/iommu/arm,smmu.txt | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.txt b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> index 7180745..4c4d03e 100644
> --- a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> +++ b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> @@ -49,6 +49,14 @@ conditions.
>                    NOTE: this only applies to the SMMU itself, not
>                    masters connected upstream of the SMMU.
>  
> +- smmu-inst-as-data : Treat privilege/unprivilege instruction fetch as
> +                  data read for SMMUv2. The SMMU driver by default provides
> +                  unprivilege read-write permission in page table entries.
> +                  For SMMUv2, privilege instruction fetch from MMU masters
> +                  will cause a context fault for unprivilege read-write
> +                  pages. To allow both privilege and unprivilege instruction
> +                  fetch, we have to forcefully treat it as data read.

What is this needed for? Which masters do instruction fetches through
the SMMU, and when?

Surely this should only need to aplly to a subset of transactions?

Mark.

> +
>  - calxeda,smmu-secure-config-access : Enable proper handling of buggy
>                    implementations that always use secure access to
>                    SMMU configuration registers. In this case non-secure
> -- 
> 1.9.1
> 
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> -----Original Message-----
> From: Mark Rutland [mailto:mark.rutland@arm.com]
> Sent: 27 January 2016 17:59
> To: Anup Patel
> Cc: Catalin Marinas; Joerg Roedel; Will Deacon; Robin Murphy; Sricharan R;
> Linux IOMMU; Linux ARM Kernel; Rob Herring; Pawel Moll; Ian Campbell; Kumar
> Gala; Device Tree; Ray Jui; Scott Branden; Vikram Prakash; Linux Kernel; bcm-
> kernel-feedback-list
> Subject: Re: [RFC PATCH 6/6] iommu/arm-smmu: Update bindings document for
> smmu-inst-as-data DT option
> 
> On Wed, Jan 27, 2016 at 10:51:19AM +0530, Anup Patel wrote:
> > This patch adds info about 'smmu-inst-as-data' DT option in ARM
> > SMMUv1/SMMUv2 driver bindings document.
> >
> > Signed-off-by: Anup Patel <anup.patel@broadcom.com>
> > Reviewed-by: Ray Jui <rjui@broadcom.com>
> > Reviewed-by: Vikram Prakash <vikramp@broadcom.com>
> > Reviewed-by: Scott Branden <sbranden@broadcom.com>
> > ---
> >  Documentation/devicetree/bindings/iommu/arm,smmu.txt | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> > b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> > index 7180745..4c4d03e 100644
> > --- a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> > +++ b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> > @@ -49,6 +49,14 @@ conditions.
> >                    NOTE: this only applies to the SMMU itself, not
> >                    masters connected upstream of the SMMU.
> >
> > +- smmu-inst-as-data : Treat privilege/unprivilege instruction fetch as
> > +                  data read for SMMUv2. The SMMU driver by default provides
> > +                  unprivilege read-write permission in page table entries.
> > +                  For SMMUv2, privilege instruction fetch from MMU masters
> > +                  will cause a context fault for unprivilege read-write
> > +                  pages. To allow both privilege and unprivilege instruction
> > +                  fetch, we have to forcefully treat it as data read.
> 
> What is this needed for? Which masters do instruction fetches through the
> SMMU, and when?
> 
> Surely this should only need to aplly to a subset of transactions?

The boot_manager of PL330 does privileged instruction fetches which
cause privilege-level context fault in SMMU because current SMMU
driver provides unprivileged read-write permissions.

Regards,
Anup

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