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SubjectRE: [PATCH] RM64: dts: ls208xa: Add iommu-map property for pci
Date
Hi Robin,

> -----Original Message-----
> From: Robin Murphy [mailto:robin.murphy@arm.com]
> Sent: Friday, September 01, 2017 4:29 PM
> To: Bharat Bhushan <bharat.bhushan@nxp.com>; Marc Zyngier
> <marc.zyngier@arm.com>; robh+dt@kernel.org; Mark Rutland
> <mark.rutland@arm.com>; will.deacon@arm.com; oss@buserror.net; Gang
> Liu <gang.liu@nxp.com>; devicetree@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> catalin.marinas@arm.com
> Subject: Re: [PATCH] RM64: dts: ls208xa: Add iommu-map property for pci
>
> On 01/09/17 11:13, Bharat Bhushan wrote:
> >
> >
> >> -----Original Message----- From: linux-kernel-owner@vger.kernel.org
> >> [mailto:linux-kernel- owner@vger.kernel.org] On Behalf Of Bharat
> >> Bhushan Sent: Thursday, August 31, 2017 4:53 PM To: Marc Zyngier
> >> <marc.zyngier@arm.com>; robh+dt@kernel.org; Mark Rutland
> >> <mark.rutland@arm.com>; will.deacon@arm.com; oss@buserror.net;
> Gang
> >> Liu <gang.liu@nxp.com>; devicetree@vger.kernel.org;
> >> linux-arm-kernel@lists.infradead.org; linux- kernel@vger.kernel.org;
> >> catalin.marinas@arm.com Subject: RE:
> >> [PATCH] RM64: dts: ls208xa: Add iommu-map property for pci
> >>
> >>
> >>
> >>> -----Original Message----- From: Marc Zyngier
> >>> [mailto:marc.zyngier@arm.com] Sent: Thursday, August 31, 2017
> >>> 4:20 PM To: Bharat Bhushan <bharat.bhushan@nxp.com>;
> >>> robh+dt@kernel.org;
> >> Mark
> >>> Rutland <mark.rutland@arm.com>; will.deacon@arm.com;
> >> oss@buserror.net;
> >>> Gang Liu <gang.liu@nxp.com>; devicetree@vger.kernel.org;
> >>> linux-arm-kernel@lists.infradead.org; linux- kernel@vger.kernel.org;
> >>> catalin.marinas@arm.com Subject: Re:
> >>> [PATCH] RM64: dts: ls208xa: Add iommu-map property for pci
> >>>
> >>> [Fixing Mark's address...]
> >>>
> >>> On 31/08/17 11:41, Bharat Bhushan wrote:
> >>>>
> >>>>> -----Original Message----- From: Marc Zyngier
> >>>>> [mailto:marc.zyngier@arm.com] Sent: Thursday, August 31, 2017
> >>>>> 3:02 PM To: Bharat Bhushan <bharat.bhushan@nxp.com>;
> >>>>> robh+dt@kernel.org; ark.rutland@arm.com; will.deacon@arm.com;
> >>>>> oss@buserror.net; Gang
> >>> Liu
> >>>>> <gang.liu@nxp.com>; devicetree@vger.kernel.org; linux-arm-
> >>>>> kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> >>>>> catalin.marinas@arm.com Subject: Re: [PATCH] RM64: dts:
> >>>>> ls208xa: Add iommu-map property for pci
> >>>>>
> >>>>> On 31/08/17 10:23, Bharat Bhushan wrote:
> >>>>>> This patch adds iommu-map property for PCIe, which enables
> SMMU
> >>>>>> for these devices on LS208xA devices.
> >>>>>>
> >>>>>> Signed-off-by: Bharat Bhushan <Bharat.Bhushan@nxp.com> ---
> >>>>>> arch/arm64/boot/dts/freescale/fsl-ls208xa.dtsi | 4 ++++ 1 file
> >>>>>> changed, 4 insertions(+)
> >>>>>>
> >>>>>> diff --git
> >>>>>> a/arch/arm64/boot/dts/freescale/fsl-ls208xa.dtsi
> >>>>>> b/arch/arm64/boot/dts/freescale/fsl-ls208xa.dtsi index
> >>>>>> 94cdd30..67cf605 100644 ---
> >>>>>> a/arch/arm64/boot/dts/freescale/fsl-ls208xa.dtsi +++
> >>>>>> b/arch/arm64/boot/dts/freescale/fsl-ls208xa.dtsi @@ -606,6
> >>>>>> +606,7 @@ num-lanes = <4>; bus-range = <0x0 0xff>;
> >>>>>> msi-parent = <&its>; + iommu-map = <0 &smmu 0
> 1>; /* This
> >>>>>> is fixed-up by
> >>>>> u-boot */
> >>>>>
> >>>>> What does this do when your version of u-boot doesn't fill this in
> >>>>> for
> >> you?
> >>>>
> >>>> Good question, frankly I have not thought of this case before.
> >>>> But if we pass length = 0 in above property then no fixup happen
> >>>> with happen with older u-boot. In this case
> >>>> of_iommu_configure() will return NULL iommu-ops and it switch to
> >>>> swio-tlb. Will that work?
> >>> I really don't like this. You rely on having invalid data in the DT,
> >>> and that seems just wrong.
> >>>
> >>> Why can't u-boot just generate that property, and we leave the DT
> >>> alone?
> >>
> >> We do not have smmu phandle allowing uboot to generate this.
> >>
> >>> Or even better, you provide the right information for the few boards
> >>> that are based on this SoC, not relying on u-boot for anything that
> >>> is in the kernel tree?
> >>
> >> On our platforms we have a h/w table which converts RID->Device-Id.
> >> I will check what will happen if that table is not initialized, can
> >> RID be equal to device-id is that case. If that will be allowed than
> >> we can give right information that will work with u-boot not updating
> >> this property.
> >
> > U-boot uses a stream-id allocator and programs the h/w mapping table
> > (rid to sid mapping table). Also it updates iommu-map property
> > accordingly. But If u-boot does not update iommu-map than we cannot
> > have a valid full proof solution as stream-id allocation can change in
> > u-boot.
> >
> > So the other option of u-boot generating this entry seems correct
> > solution. This requires u-boot to know iommu-phandle, something
> > similar to "msi-parent" used for "msi-map" Device-tree binding need
> > change to add iommu-phandle/iommu-parent for this.
>
> From what I know of this hardware, it's going to be rather difficult to concoct
> a DT which reflects the initial hardware state accurately *and* works
> correctly without updating u-boot in lockstep. IIRC, I believe the accurate
> description for an unprogrammed LUT would be "everything comes out on
> the default ID, which defaults to 0", i.e.:
>
> iommu-map-mask = <0x0>;
> iommu-map = <0x0 &smmu 0x0 0x1>;

These changes are not enough to make PCI devise working with LUT disabled, also needed msi-map maps all requester-id to "0", using "msi-map-mask = 0x0".

Why we assume that no "msi-map" property means untranslated requested-id, why not consider that translated to "0".

>
> (assuming the SMMU has stream-id-mask set appropriately too)
>
> That's OK except if u-boot updates the map without removing the mask,
> whereupon things will go wrong, and I guess that would be the case with
> current u-boot :(
>
> However, the existing MSI description is already bogus - if u-boot didn't
> program the LUT, the ITS driver would treat the invalid "msi-parent" property
> as this:
>
> msi-map = <0x0 &its 0x0 0xffff>;
>
> which means that nobody other than 0:0.0 has working MSIs anyway.

We can have following version of u-boot:
1) No LUT setup, does not generate msi-map and does not update/generate iommu-map (older u-boot)

For this case the working device tree changes can be:
iommu-map-mask = <0>;
iommu-map = <0x0 &smmu 0 0x1>;
msi-map-mask = <0x0>;
msi-map = <0x0 &its 0 0x1>;

But these changes will not work with current version of u-boot (below (2))

2) LUT setup and msi-map generated but no iommu-map generated (current case)

I do not see we can have a working device tree for this.
Probably generating iommu-map in u-boot is better, with that msi-map and iommu-map will be consistent (below (4))

3) LUT setup, "msi-map" generated and iommu-map updated

We can have below change is device tree.
iommu-map = <0x0 &smmu 0 0x1>;

But this change will not work with (1) and (2) above.

4) LUT setup, "msi-map" generated and iommu-map also generated by u-boot.
There is no iommu-map entry needed in device tree but u-boot need to know iommu phandle.
While iommus is supposed to be used in iommu-node and not in pci node.

Looking for suggestion

Thanks
-Bharat

>
> If you want an obviously-invalid placeholder equivalent to the use of "msi-
> parent" then I'd suggest just:
>
> iommus = <&smmu>;
>
> which would be ignored by Linux for PCI devices, so provided you didn't
> disable bypass at the SMMU things might in theory still work in the "u-boot
> does nothing" case. Otherwise, the implied identity map is probably slightly
> preferable to the unit-length map, i.e.:
>
> iommu-map = <0x0 &smmu 0x0 0xffff>;
>
> which is at least equally broken as MSIs in the same situation.
>
> Robin.
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