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Date: Mon, 15 Jan 2024 15:45:37 +0100
From: Maxime Ripard <mripard@kernel.org>
To: "H. Nikolaus Schaller" <hns@goldelico.com>
Cc: Andrew Davis <afd@ti.com>, Frank Binns <frank.binns@imgtec.com>, 
	Donald Robson <donald.robson@imgtec.com>, Matt Coster <matt.coster@imgtec.com>, 
	Adam Ford <aford173@gmail.com>, Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>, 
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>, Thomas Zimmermann <tzimmermann@suse.de>, 
	Rob Herring <robh+dt@kernel.org>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>, 
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	=?utf-8?Q?Beno=C3=AEt?= Cousson <bcousson@baylibre.com>, Tony Lindgren <tony@atomide.com>, Nishanth Menon <nm@ti.com>, 
	Vignesh Raghavendra <vigneshr@ti.com>, Tero Kristo <kristo@kernel.org>, 
	Paul Cercueil <paul@crapouillou.net>, dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, 
	linux-sunxi@lists.linux.dev, linux-omap@vger.kernel.org, linux-mips@vger.kernel.org
Subject: Re: Re: [PATCH RFC v2 04/11] ARM: dts: omap4: Add device tree entry
 for SGX GPU
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References: <20240108183302.255055-1-afd@ti.com>
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On Mon, Jan 15, 2024 at 09:55:00AM +0100, H. Nikolaus Schaller wrote:
> Hi,
>=20
> > Am 15.01.2024 um 09:25 schrieb Maxime Ripard <mripard@kernel.org>:
> >=20
> > Hi,
> >=20
> > On Fri, Jan 12, 2024 at 06:33:58PM +0100, H. Nikolaus Schaller wrote:
> >>> Am 08.01.2024 um 19:32 schrieb Andrew Davis <afd@ti.com>:
> >>>=20
> >>> Add SGX GPU device entry to base OMAP4 dtsi file.
> >>>=20
> >>> Signed-off-by: Andrew Davis <afd@ti.com>
> >>> ---
> >>> arch/arm/boot/dts/ti/omap/omap4.dtsi | 9 +++++----
> >>> 1 file changed, 5 insertions(+), 4 deletions(-)
> >>>=20
> >>> diff --git a/arch/arm/boot/dts/ti/omap/omap4.dtsi b/arch/arm/boot/dts=
/ti/omap/omap4.dtsi
> >>> index 2bbff9032be3e..559b2bfe4ca7c 100644
> >>> --- a/arch/arm/boot/dts/ti/omap/omap4.dtsi
> >>> +++ b/arch/arm/boot/dts/ti/omap/omap4.dtsi
> >>> @@ -501,10 +501,11 @@ sgx_module: target-module@56000000 {
> >>> #size-cells =3D <1>;
> >>> ranges =3D <0 0x56000000 0x2000000>;
> >>>=20
> >>> - /*
> >>> - * Closed source PowerVR driver, no child device
> >>> - * binding or driver in mainline
> >>> - */
> >>> + gpu@0 {
> >>=20
> >> I wonder why we don't add a "gpu:" label here.
> >>=20
> >> Almost all other subsystem nodes have one (e.g. emif:, aes:, dss:, dsi=
:, hdmi:, etc.),
> >> obviously for convenience when using a .dtsi file.
> >>=20
> >> It would allow a board-specific DTS to easily add status =3D "disabled=
" to avoid driver
> >> probing or disabling the GPU (e.g. if there is no display).
> >=20
> > There's no reason to disable it in the DT: the hardware block would
> > still be there and it's rendering to memory so it still could be useful.
>=20
> Well, if you know that the board does not have a dm3730 but a dm3725 with=
out
> GPU it is better to disable the GPU completely instead of loading the dri=
ver
> and make it detect by some internal bits that it has no GPU on the SoC.

It shouldn't even be in the DTSI if it's not in the SoC.

> > If there's no display on the board and you really don't want the GPU
> > driver, then you can disable the driver or block the module loading, but
> > it should be a distro / package / user decision, not a DT / kernel one
> > still.
>=20
> The same holds for aes: dss: dsi: hdmi: etc. If they are not used by some
> board file, they don't change a single bit of the DTB [1] which IMHO would
> be of reasonable concern to question additional labels.

Not really, no. If there's no HDMI connector, the HDMI controller is
useless. A GPU without a display can still be useful, depending on the
workload.

Maxime

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