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Subject: Re: [PATCH RFC v2 04/11] ARM: dts: omap4: Add device tree entry for
 SGX GPU
From: "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <vpcgccul53oibwoqb3barj3rjxoyskoldjyfvjdzmytic3tonm@wq4aqsenk7rp>
Date: Mon, 15 Jan 2024 09:55:00 +0100
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>,
 Conor Dooley <conor+dt@kernel.org>,
 Chen-Yu Tsai <wens@csie.org>,
 Jernej Skrabec <jernej.skrabec@gmail.com>,
 Samuel Holland <samuel@sholland.org>,
 =?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,
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References: <20240108183302.255055-1-afd@ti.com>
 <20240108183302.255055-5-afd@ti.com>
 <122DC5ED-2AA7-46A0-845F-083922458385@goldelico.com>
 <vpcgccul53oibwoqb3barj3rjxoyskoldjyfvjdzmytic3tonm@wq4aqsenk7rp>
To: Maxime Ripard <mripard@kernel.org>

Hi,

> 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.

Well, if you know that the board does not have a dm3730 but a dm3725 =
without
GPU it is better to disable the GPU completely instead of loading the =
driver
and make it detect by some internal bits that it has no GPU on 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.

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.

BR and thanks,
Nikolaus

[1] =
https://devicetree-specification.readthedocs.io/en/stable/source-language.=
html
"Labels are only used in the devicetree source format and are not =
encoded into the
DTB binary."