linux-kernel - Re: [PATCH 8/9] drm/rockchip: Drop ROCKCHIP_IOMMU depend for DRM

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Message-ID: <2629918.TLnPLrj5Ze@diego>
Date: Fri, 09 Jan 2026 11:51:49 +0100
From: Heiko Stübner <heiko@...ech.de>
To: Neil Armstrong <neil.armstrong@...aro.org>,
 Jessica Zhang <jessica.zhang@....qualcomm.com>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Sandy Huang <hjc@...k-chips.com>,
 Andy Yan <andy.yan@...k-chips.com>, Vinod Koul <vkoul@...nel.org>,
 Kishon Vijay Abraham I <kishon@...nel.org>, Chaoyi Chen <kernel@...kyi.com>,
 Chaoyi Chen <chaoyi.chen@...k-chips.com>
Cc: dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org, linux-phy@...ts.infradead.org
Subject:
 Re: [PATCH 8/9] drm/rockchip: Drop ROCKCHIP_IOMMU depend for DRM_ROCKCHIP

Hi,

Am Freitag, 9. Januar 2026, 02:26:00 Mitteleuropäische Normalzeit schrieb Chaoyi Chen:
> On 1/9/2026 3:03 AM, Heiko Stuebner wrote:
> > Am Donnerstag, 6. November 2025, 03:06:31 Mitteleuropäische Normalzeit schrieb Chaoyi Chen:
> >> From: Chaoyi Chen <chaoyi.chen@...k-chips.com>
> >>
> >> On the RK3506 platform, there is no iommu hardware. And even on
> >> platform that have iommu hardware, it should be possible to use
> >> VOP without enabling iommu. In this case, a contiguous memory
> >> space like CMA should be used.
> >>
> >> So this patch removes the dependency on ROCKCHIP_IOMMU.
> >>
> >> Signed-off-by: Chaoyi Chen <chaoyi.chen@...k-chips.com>
> >> ---
> >>  drivers/gpu/drm/rockchip/Kconfig | 3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/rockchip/Kconfig b/drivers/gpu/drm/rockchip/Kconfig
> >> index b7b025814e72..a056d419190c 100644
> >> --- a/drivers/gpu/drm/rockchip/Kconfig
> >> +++ b/drivers/gpu/drm/rockchip/Kconfig
> >> @@ -1,7 +1,8 @@
> >>  # SPDX-License-Identifier: GPL-2.0-only
> >>  config DRM_ROCKCHIP
> >>  	tristate "DRM Support for Rockchip"
> >> -	depends on DRM && ROCKCHIP_IOMMU
> >> +	depends on DRM
> >> +	depends on ROCKCHIP_IOMMU || !ROCKCHIP_IOMMU
> > 
> > I don't really understand this yes+no line :-)
> > 
> > Can't you just
> > - drop the dependency altogether
> > or
> > - do a depends on ROCKCHIP_IOMMU if ARM64
> > 
> >
> 
> This trick is called optional-dependencies [0]. In addition to the 
> familiar depends on ROCKCHIP_IOMMU part, the newly added !ROCKCHIP_IOMMU
> ensures that DRM_ROCKCHIP can still be built even when ROCKCHIP_IOMMU
> is not build.
> 
> [0]: https://docs.kernel.org/kbuild/kconfig-language.html#optional-dependencies

thanks a lot for pointing me to this nifty feature :-)

Heiko