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

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Date:	Thu, 12 May 2016 12:46:15 +0200
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	airlied@...hat.com, David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Matthias Brugger <matthias.bgg@...il.com>,
	Bibby Hsieh <bibby.hsieh@...iatek.com>,
	YT Shen <yt.shen@...iatek.com>,
	Mao Huang <littlecvr@...omium.org>, CK Hu <ck.hu@...iatek.com>,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] drm: mediatek: remove IOMMU_DMA select

Am Mittwoch, den 11.05.2016, 22:11 +0200 schrieb Arnd Bergmann:
> 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.

No, it just has been there since the initial RFC and nobody noticed.

>  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

Acked-by: Philipp Zabel <p.zabel@...gutronix.de>

I tried
  make ARCH=arm64 allnoconfig
and then set
  CONFIG_MODULES=y
  CONFIG_ARCH_MEDIATEK=y
  CONFIG_DRM=m
  CONFIG_DRM_MEDIATEK=m

And it builds fine with IOMMU_DMA/MTK_IOMMU disabled.

thanks
Philipp