linux-kernel - [RFC 0/3] iommu/samsung: Introduce Exynos sysmmu-v8 driver

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Date:   Thu, 20 Jan 2022 22:19:55 +0200
From:   Sam Protsenko <semen.protsenko@...aro.org>
To:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Cho KyongHo <pullip.cho@...sung.com>,
        Hyesoo Yu <hyesoo.yu@...sung.com>,
        Janghyuck Kim <janghyuck.kim@...sung.com>,
        Jinkyu Yang <jinkyu1.yang@...sung.com>,
        Alex <acnwigwe@...gle.com>, Carlos Llamas <cmllamas@...gle.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        Erick Reyes <erickreyes@...gle.com>,
        "J . Avila" <elavila@...gle.com>, Jonglin Lee <jonglin@...gle.com>,
        Mark Salyzyn <salyzyn@...gle.com>,
        Thierry Strudel <tstrudel@...gle.com>,
        Will McVicker <willmcvicker@...gle.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-samsung-soc@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [RFC 0/3] iommu/samsung: Introduce Exynos sysmmu-v8 driver

This is a draft of a new IOMMU driver used in modern Exynos SoCs (like
Exynos850) and Google's GS101 SoC (used in Pixel 6 phone). Most of its
code were taken from GS101 downstream kernel [1], with some extra
patches on top (fixes from Exynos850 downstream kernel and some porting
changes to adapt it to the mainline kernel). All development history can
be found at [2].

Similarities with existing exynos-iommu.c is minimal. I did some
analysis using similarity-tester tool:

8<-------------------------------------------------------------------->8
    $ sim_c -peu -S exynos-iommu.c "|" samsung-*

    exynos-iommu.c consists for 15 % of samsung-iommu.c material
    exynos-iommu.c consists for 1 %  of samsung-iommu-fault.c material
    exynos-iommu.c consists for 3 %  of samsung-iommu.h material
8<-------------------------------------------------------------------->8

So the similarity is very low, most of that code is some boilerplate
that shouldn't be extracted to common code (like allocating the memory
and requesting clocks/interrupts in probe function).

It was tested on v5.4 Android kernel on Exynos850 (E850-96 board) with
DPU use-case (displaying some graphics to the screen). Also it
apparently works fine on v5.10 GS101 kernel (on Pixel 6). On mainline
kernel I managed to build, match and bind the driver. No real world test
was done, but the changes from v5.10 (where it works fine) are minimal
(see [2] for details). So I'm pretty sure the driver is functional.

For this patch series I'd like to receive some high-level review for
driver's design and architecture. Coding style and API issues I can fix
later, when sending real (not RFC) series. Particularly I'd like to hear
some opinions about:
  - namings: Kconfig option, file names, module name, compatible, etc
  - modularity: should this driver be a different platform driver (like
    in this series), or should it be integrated into existing
    exynos-iommu.c driver somehow
  - dt-bindings: does it look ok as it is, or some interface changes are
    needed
  - internal driver architecture: approach seems to be similar to
    exynos-iommu.c, but any comments are welcome
  - ongoing work: please let me know if you're aware of some efforts to
    upstream this driver by some other party (e.g. Google engineers
    might be working on something similar)

Basically, I want to figure out what should be changed/fixed in this
driver (on a high level), so it can be considered "upstreamable".

[1] https://android.googlesource.com/kernel/gs/
[2] https://github.com/joe-skb7/linux/commits/iommu-exynos850-dev

Sam Protsenko (3):
  dt-bindings: iommu: Add bindings for samsung,sysmmu-v8
  iommu/samsung: Introduce Exynos sysmmu-v8 driver
  arm64: defconfig: Enable sysmmu-v8 IOMMU

 .../bindings/iommu/samsung,sysmmu-v8.txt      |   31 +
 arch/arm64/configs/defconfig                  |    2 +
 drivers/iommu/Kconfig                         |   13 +
 drivers/iommu/Makefile                        |    3 +
 drivers/iommu/samsung-iommu-fault.c           |  617 +++++++
 drivers/iommu/samsung-iommu-group.c           |   50 +
 drivers/iommu/samsung-iommu.c                 | 1521 +++++++++++++++++
 drivers/iommu/samsung-iommu.h                 |  216 +++
 include/dt-bindings/soc/samsung,sysmmu-v8.h   |   43 +
 9 files changed, 2496 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iommu/samsung,sysmmu-v8.txt
 create mode 100644 drivers/iommu/samsung-iommu-fault.c
 create mode 100644 drivers/iommu/samsung-iommu-group.c
 create mode 100644 drivers/iommu/samsung-iommu.c
 create mode 100644 drivers/iommu/samsung-iommu.h
 create mode 100644 include/dt-bindings/soc/samsung,sysmmu-v8.h

-- 
2.30.2