Re: [PATCH 3/3] arm64: dts: allwinner: h6: Add IOMMU

From: Maxime Ripard <maxime@cerno.tech>
To: "Jernej Škrabec" <jernej.skrabec@gmail.com>
Cc: Joerg Roedel <joro@8bytes.org>, Chen-Yu Tsai <wens@csie.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
	iommu@lists.linux-foundation.org
Subject: Re: [PATCH 3/3] arm64: dts: allwinner: h6: Add IOMMU
Date: Wed, 29 Jan 2020 18:27:38 +0100	[thread overview]
Message-ID: <20200129172738.c53f5du2byreze2n@gilmour.lan> (raw)
In-Reply-To: <2140600.ElGaqSPkdT@jernej-laptop>

Hi,

On Mon, Jan 27, 2020 at 08:04:02PM +0100, Jernej Škrabec wrote:
> Dne ponedeljek, 27. januar 2020 ob 15:23:39 CET je Maxime Ripard napisal(a):
> > Hi Jernej,
> >
> > On Fri, Jan 24, 2020 at 09:54:23PM +0100, Jernej Škrabec wrote:
> > > Dne sreda, 22. januar 2020 ob 13:44:09 CET je Maxime Ripard napisal(a):
> > > > Now that we have a driver for the IOMMU, let's start using it.
> > > >
> > > > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > > > ---
> > > >
> > > >  arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi | 11 +++++++++++
> > > >  1 file changed, 11 insertions(+)
> > > >
> > > > diff --git a/arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi
> > > > b/arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi index
> > > > 29824081b43b..8608bcf1c52c 100644
> > > > --- a/arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi
> > > > +++ b/arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi
> > > > @@ -53,6 +53,7 @@
> > > >
> > > >  	de: display-engine {
> > > >
> > > >  		compatible = "allwinner,sun50i-h6-display-engine";
> > > >  		allwinner,pipelines = <&mixer0>;
> > > >
> > > > +		iommus = <&iommu 0>;
> > > >
> > > >  		status = "disabled";
> > > >
> > > >  	};
> > >
> > > Isn't iommu property of the mixer node? After all, mixer is the one which
> > > reads one or more framebuffers. Once second mixer is defined, would you
> > > put
> > > another iommu phandle here?
> >
> > You're right. I added it during the early dev, and forgot to remove
> > it. Thanks!
>
> Remove it or move it? I guess enabling iommu support in each driver needs a
> bit more work than just referencing iommu node, right? At least in such case
> buffers don't need to be allocated by CMA, which sun4i-drm driver currently
> use.
>
> I just take another look at BSP kernel and it seems that only one channel is
> used for whole display stack. That would mean that both mixers would have same
> iommu phandle, right? Confusingly enough, DE2 iommu channel seems to be for
> deinterlace core.

To add on Robin's answer, yeah, it looks like the display engine is
called DE (and I've checked that this is indeed the master 0), while
the deinterlace is called DE2 (and probably is the master 2).

Maxime