linux-kernel - Re: [PATCH v5 0/5] iommu: M1 Pro/Max DART support

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Date:   Wed, 21 Sep 2022 14:20:40 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Konrad Dybcio <konrad.dybcio@...ainline.org>,
        asahi@...ts.linux.dev, Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Hector Martin <marcan@...can.st>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Rob Herring <robh+dt@...nel.org>,
        Sven Peter <sven@...npeter.dev>, Will Deacon <will@...nel.org>,
        devicetree@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux.dev, Janne Grunau <j@...nau.net>
Subject: Re: [PATCH v5 0/5] iommu: M1 Pro/Max DART support

On 2022-09-16 10:41, Janne Grunau wrote:
> Hej,
> 
> this is the next attempt adding support for the DART found in Apple's
> M1 Pro/Max/Ultra. This adds a separate io-pgtable implementation for
> DART. As already mentioned in v2 the pte format is not fully compatible
> with io-pgtable-arm. Especially the 2nd least significant bit is used
> and is not available to tag tables/pages.
> io-pgtable-dart.c is copied from io-pgtable-arm.c and support for
> unused features is removed. Support for 4k IO pages is left for A7 to
> A11 SoCs as there's work underway to run Linux on them.
> 
> The incompatibilities between both Apple DART pte seems manageable in
> their own io-pgtable implementation. A short list of the known
> differences:
> 
>   - the physical addresses are shifted left by 4 bits and and have 2 more
>     bits inside the PTE entries
>   - the read/write protection flags are at a different position
>   - the subpage protection feature is now mandatory. For Linux we can
>     just configure it to always allow access to the entire page.
>   - BIT(1) tags "uncached" mappings (used for the display controller)
> 
> There is second type of DART (t8110) present on M1 Pro/Max SoCs which
> uses the same PTE format as t6000.

FWIW I think there's minimal risk in queueing this up as a late addition 
for 6.1, lest it get forgotten again. I've not been following it since 
I've been busy with other things and I largely trust that DART patches 
are well-tested, but from a quick skim it all earns a solid "yeah, why 
not" from me :)

Cheers,
Robin.

> Changes in v5:
> - collected Sven's ack
> - minor fixes in "iommu/io-pgtable: Move Apple DART support to its own
>    file"
> 
> Changes in v4:
> - split dart and io-pgtable-dart build to allow building dart as module
> - add missing "SELECT IOMMU_IO_PGTABLE"
> - made map/unmap_pages/iova_to_phys inon-recursive
> - replace pgd concatenation with multiple table handling
> - simplified config and page size checks
> - collected Robin's Ack
> 
> Changes in v3:
> - move APPLE_DART to its own io-pgtable implementation, copied from
>    io-pgtable-arm and simplified
> 
> Changes in v2:
> - added Rob's Acked-by:
> - add APPLE_DART2 io-pgtable format
> 
> Janne Grunau (1):
>    iommu/io-pgtable: Move Apple DART support to its own file
> 
> Sven Peter (4):
>    dt-bindings: iommu: dart: add t6000 compatible
>    iommu/io-pgtable: Add DART subpage protection support
>    iommu/io-pgtable-dart: Add DART PTE support for t6000
>    iommu: dart: Support t6000 variant
> 
>   .../devicetree/bindings/iommu/apple,dart.yaml |   4 +-
>   MAINTAINERS                                   |   1 +
>   drivers/iommu/Kconfig                         |  13 +-
>   drivers/iommu/Makefile                        |   1 +
>   drivers/iommu/apple-dart.c                    |  24 +-
>   drivers/iommu/io-pgtable-arm.c                |  63 ---
>   drivers/iommu/io-pgtable-dart.c               | 470 ++++++++++++++++++
>   drivers/iommu/io-pgtable.c                    |   3 +
>   include/linux/io-pgtable.h                    |   1 +
>   9 files changed, 512 insertions(+), 68 deletions(-)
>   create mode 100644 drivers/iommu/io-pgtable-dart.c
>