linux-kernel - Re: [PATCH] drm: mediatek: remove IOMMU

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Date:	Thu, 12 May 2016 10:24:02 +0100
From:	Robin Murphy <robin.murphy@....com>
To:	Arnd Bergmann <arnd@...db.de>, airlied@...hat.com,
	David Airlie <airlied@...ux.ie>
Cc:	Bibby Hsieh <bibby.hsieh@...iatek.com>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Mao Huang <littlecvr@...omium.org>,
	YT Shen <yt.shen@...iatek.com>, CK Hu <ck.hu@...iatek.com>,
	linux-mediatek@...ts.infradead.org,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Matthias Brugger <matthias.bgg@...il.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] drm: mediatek: remove IOMMU_DMA select

On 11/05/16 21:11, Arnd Bergmann wrote:
> We get a harmless build warning when trying to use the mediatek
> DRM driver with IOMMU support disabled:
>
> warning: (DRM_MEDIATEK) selects IOMMU_DMA which has unmet direct dependencies (IOMMU_SUPPORT)
>
> However, the IOMMU_DMA symbol is not meant to be used by drivers
> at all, and this driver doesn't seem to have a strict dependency
> on it other than using the mediatek IOMMU driver that does.
>
> Since we also want to be able to do compile tests with the
> driver on other platforms, the IOMMU_DMA symbol should not
> be selected here.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> If someone has a better explanation about why the 'select' is here,
> let me know, it certainly seems out of place.

Ack - it's neither an IOMMU driver nor a DMA API implementation, so it 
has no business with IOMMU_DMA. If there's an IOMMU dependency in 
general it should be on MTK_IOMMU, not underlying implementation details.

Robin.

>   drivers/gpu/drm/mediatek/Kconfig | 1 -
>   1 file changed, 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/mediatek/Kconfig b/drivers/gpu/drm/mediatek/Kconfig
> index 0c06a69d7f04..545973f6b743 100644
> --- a/drivers/gpu/drm/mediatek/Kconfig
> +++ b/drivers/gpu/drm/mediatek/Kconfig
> @@ -7,7 +7,6 @@ config DRM_MEDIATEK
>   	select DRM_KMS_HELPER
>   	select DRM_MIPI_DSI
>   	select DRM_PANEL
> -	select IOMMU_DMA
>   	select MEMORY
>   	select MTK_SMI
>   	help
>