linux-kernel - Re: [PATCH v2 0/6] iommu/exynos: Convert to a module

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Date:   Fri, 4 Nov 2022 13:10:02 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Janghyuck Kim <janghyuck.kim@...sung.com>,
        Cho KyongHo <pullip.cho@...sung.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        David Virag <virag.david003@...il.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH v2 0/6] iommu/exynos: Convert to a module

On 03.11.2022 20:51, Sam Protsenko wrote:
> As exynos-iommu driver is not a critical platform driver, it can be
> converted to a loadable module to avoid loading it on non-Exynos
> platforms in order to improve the RAM footprint. This patch series
> converts it to a module and does some related cleanups. IOMMU/DMA
> specifics were taken into the account, so remove/exit methods weren't
> added.
>
> There are two drivers using CONFIG_EXYNOS_IOMMU in their code:
> DRM_EXYNOS and S5P_MFC. Both were checked, and only a slight change was
> needed for S5P_MFC driver (patch #6).

Funny, compiling this driver as a module revealed an issue in the driver 
initialization sequence, here is a fix that need to be applied before 
this patchset:

https://lore.kernel.org/all/20221104115511.28256-1-m.szyprowski@samsung.com/

Besides that, the driver nukes with NULL pointer dereference in 
exynos_iommu_of_xlate() when compiled as a module on ARM 64bit 
Exynos5433 based TM2e board. ARM 32bit based board works fine. I'm 
checking this issue now.

> Changes in v2:
>    - Extracted the "shutdown" method addition into a separate patch
>    - Added MODULE_DEVICE_TABLE(of, ...) to support hot-plug loading
>    - Added MODULE_ALIAS("platform:exynos-sysmmu")
>    - Added fix for S5P_MFC driver to work correctly with EXYNOS_IOMMU=m
>    - Fixed checkpatch coding style suggestion with "--strict" flag
>    - Rebased on top of most recent joro/iommu.git:next
>
> Sam Protsenko (6):
>    iommu: Export iommu_group_default_domain() API
>    iommu/exynos: Fix retval on getting clocks in probe
>    iommu/exynos: Modularize the driver
>    iommu/exynos: Implement shutdown driver method
>    iommu/exynos: Rearrange the platform driver code
>    media: platform: Use IS_ENABLED() to check EXYNOS_IOMMU in s5p_mfc
>
>   drivers/iommu/Kconfig                         |   2 +-
>   drivers/iommu/exynos-iommu.c                  | 355 +++++++++---------
>   drivers/iommu/iommu.c                         |   1 +
>   .../platform/samsung/s5p-mfc/s5p_mfc_iommu.h  |   4 +-
>   4 files changed, 191 insertions(+), 171 deletions(-)
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland