linux-kernel - Re: Re: [PATCH RFC v2 04/11] ARM: dts: omap4: Add device tree entry for SGX GPU

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Message-ID: <xagwa5cie5gjzidg5wa6ou3yd2qwta7ridci4jzkrpcccm24mz@aphgjsdytirz>
Date: Mon, 15 Jan 2024 15:45:37 +0100
From: Maxime Ripard <mripard@...nel.org>
To: "H. Nikolaus Schaller" <hns@...delico.com>
Cc: Andrew Davis <afd@...com>, Frank Binns <frank.binns@...tec.com>, 
	Donald Robson <donald.robson@...tec.com>, Matt Coster <matt.coster@...tec.com>, 
	Adam Ford <aford173@...il.com>, Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	Rob Herring <robh+dt@...nel.org>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
	Conor Dooley <conor+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, 
	Benoît Cousson <bcousson@...libre.com>, Tony Lindgren <tony@...mide.com>, Nishanth Menon <nm@...com>, 
	Vignesh Raghavendra <vigneshr@...com>, Tero Kristo <kristo@...nel.org>, 
	Paul Cercueil <paul@...pouillou.net>, dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-sunxi@...ts.linux.dev, linux-omap@...r.kernel.org, linux-mips@...r.kernel.org
Subject: Re: Re: [PATCH RFC v2 04/11] ARM: dts: omap4: Add device tree entry
 for SGX GPU

On Mon, Jan 15, 2024 at 09:55:00AM +0100, H. Nikolaus Schaller wrote:
> Hi,
> 
> > Am 15.01.2024 um 09:25 schrieb Maxime Ripard <mripard@...nel.org>:
> > 
> > Hi,
> > 
> > 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@...com>:
> >>> 
> >>> Add SGX GPU device entry to base OMAP4 dtsi file.
> >>> 
> >>> Signed-off-by: Andrew Davis <afd@...com>
> >>> ---
> >>> arch/arm/boot/dts/ti/omap/omap4.dtsi | 9 +++++----
> >>> 1 file changed, 5 insertions(+), 4 deletions(-)
> >>> 
> >>> 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@...00000 {
> >>> #size-cells = <1>;
> >>> ranges = <0 0x56000000 0x2000000>;
> >>> 
> >>> - /*
> >>> - * Closed source PowerVR driver, no child device
> >>> - * binding or driver in mainline
> >>> - */
> >>> + gpu@0 {
> >> 
> >> I wonder why we don't add a "gpu:" label here.
> >> 
> >> Almost all other subsystem nodes have one (e.g. emif:, aes:, dss:, dsi:, hdmi:, etc.),
> >> obviously for convenience when using a .dtsi file.
> >> 
> >> It would allow a board-specific DTS to easily add status = "disabled" to avoid driver
> >> probing or disabling the GPU (e.g. if there is no display).
> > 
> > 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.

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.
> 
> 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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