linux-kernel - Re: [PATCH v2 4/7] ARM: dts: rockchip: add virtual iommu for display

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Message-ID: <CAAFQd5AU2xV98bAEDvPpV1-5ED3oCMgp9vuTymX-RpWFVhH=mw@mail.gmail.com>
Date:	Fri, 10 Jun 2016 15:22:56 +0900
From:	Tomasz Figa <tfiga@...omium.org>
To:	Shunqian Zheng <zhengsq@...k-chips.com>
Cc:	Joerg Roedel <joro@...tes.org>,
	Heiko Stübner <heiko@...ech.de>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>, linux@...linux.org.uk,
	姚智情 <mark.yao@...k-chips.com>,
	David Airlie <airlied@...ux.ie>,
	simon xue <xxm@...k-chips.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
	devicetree@...r.kernel.org,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH v2 4/7] ARM: dts: rockchip: add virtual iommu for display

Hi,

On Wed, Jun 8, 2016 at 10:26 PM, Shunqian Zheng <zhengsq@...k-chips.com> wrote:
> An virtual iommu without reg or interrupts for display.
> Adding this according to iommu driver changes.
>
> Signed-off-by: Shunqian Zheng <zhengsq@...k-chips.com>
> ---
>  arch/arm/boot/dts/rk3288.dtsi | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm/boot/dts/rk3288.dtsi b/arch/arm/boot/dts/rk3288.dtsi
> index 7fa932f..4cd535f 100644
> --- a/arch/arm/boot/dts/rk3288.dtsi
> +++ b/arch/arm/boot/dts/rk3288.dtsi
> @@ -219,9 +219,15 @@
>                 clock-names = "timer", "pclk";
>         };
>
> +       display_mmu: virtual-iommu {
> +               compatible = "rockchip,iommu";
> +               #iommu-cells = <0>;
> +       };
> +

Device tree should describe real hardware and so it isn't really a
good idea to add such virtual iommu, especially using a compatible
string of a real device.

Please see my comments to patch 3/7 for an alternative idea.

Best regards,
Tomasz