linux-kernel - Re: [PATCH 1/1] ARM: exynos_defconfig: Disable IOMMU support

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Date:	Tue, 17 Feb 2015 13:56:25 +0100
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
CC:	Kukjin Kim <kgene@...nel.org>, Olof Johansson <olof@...om.net>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Andreas Faerber <afaerber@...e.de>,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ARM: exynos_defconfig: Disable IOMMU support

Hello Krzysztof,

On 02/17/2015 01:20 PM, Krzysztof Kozlowski wrote:
> On wto, 2015-02-17 at 12:38 +0100, Javier Martinez Canillas wrote:
>> Enabling Exynos DRM IOMMU support for Exynos is currently broken and
>> causes a BUG on exynos-iommu driver. This was not an issue since the
>> options was disabled in exynos_defconfig but after commit 8dcc14f82f06
>> ("drm/exynos: IOMMU support should not be selectable by user"), it is
>> selected if EXYNOS_IOMMU is enabled which is in exynos_defconfig.
>> 
>> So a kernel built using exynos_defconfig after the mentioned commit
>> fails to boot [0]. Disable IOMMU support in Exynos defconfig until
>> things get sorted out.
> 
> On which board you got this error?
> 

Sorry, I should had mention it in the commit message. I get that error
with at least Exynos5800 Peach Pi, Exynos5420 Peach Pit and Exynos5250
Snow Chromebooks with today's next (next-20150217).

The problem is that the Exynos IOMMU driver does not set a struct
exynos_iommu_owner in dev.archdata.iommu but __exynos_sysmmu_enable()
has a BUG_ON(!has_sysmmu(dev)).

Marek's series [1] solves this issue by filling sysmmu devices from DT
but causes boot failures on the Exynos Chromebooks because the display
is left enabled by the bootloader [2].

So I think that this option should be disabled until is known to not
cause issues on any platform.

> Best regards,
> Krzysztof
>

[1]: http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/319244.html
[2]: http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/319293.html
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