linux-kernel - Re: [RFC PATCH 3/3] arm64: dts: ti: k3-am62x: Add overlay to use DSS in display sharing mode

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Message-ID: <e452c6ae-e889-44a9-9fbf-99527f5c50b9@ideasonboard.com>
Date: Tue, 23 Jan 2024 10:29:37 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Devarsh Thakkar <devarsht@...com>
Cc: praneeth@...com, a-bhatia1@...com, j-luthra@...com, jyri.sarha@....fi,
 airlied@...il.com, daniel@...ll.ch, maarten.lankhorst@...ux.intel.com,
 mripard@...nel.org, tzimmermann@...e.de, robh+dt@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 nm@...com, vigneshr@...com, kristo@...nel.org
Subject: Re: [RFC PATCH 3/3] arm64: dts: ti: k3-am62x: Add overlay to use DSS
 in display sharing mode

Hi,

On 16/01/2024 15:41, Devarsh Thakkar wrote:
> This overlay needs to be used with display sharing supported device
> manager firmware only.
> 
> Remote core running this firmware has write access to "common" register
> space, VIDL pipeline, OVR1 overlay and VP1 videoport.
> 
> The processing core running Linux is provided write access to VID
> pipeline and "common1" register space.
> 
> The VP1 video port is shared between Linux and remote core with remote
> core configuring the overlay manager to set Zorder 1 for VID pipeline
> and Zorder 2 for VIDL pipeline.
> 
> Add reserved memory region for framebuffer region used by remote core in
> dss shared mode overlay file so that Linux does not re-use the same
> while allocating memory.

I don't understand this one. Why is RAM used by RTOS accessible by Linux 
in the first place?

  Tomi

> Also add a label for reserved memory region in base device-tree file so
> that it can be referred back in overlay file.
> 
> Signed-off-by: Devarsh Thakkar <devarsht@...com>
> ---
>   arch/arm64/boot/dts/ti/Makefile               |  1 +
>   .../arm64/boot/dts/ti/k3-am62x-sk-common.dtsi |  2 +-
>   .../dts/ti/k3-am62x-sk-dss-shared-mode.dtso   | 33 +++++++++++++++++++
>   3 files changed, 35 insertions(+), 1 deletion(-)
>   create mode 100644 arch/arm64/boot/dts/ti/k3-am62x-sk-dss-shared-mode.dtso
> 
> diff --git a/arch/arm64/boot/dts/ti/Makefile b/arch/arm64/boot/dts/ti/Makefile
> index 52c1dc910308..ff832741b367 100644
> --- a/arch/arm64/boot/dts/ti/Makefile
> +++ b/arch/arm64/boot/dts/ti/Makefile
> @@ -35,6 +35,7 @@ dtb-$(CONFIG_ARCH_K3) += k3-am62x-sk-csi2-ov5640.dtbo
>   dtb-$(CONFIG_ARCH_K3) += k3-am62x-sk-csi2-tevi-ov5640.dtbo
>   dtb-$(CONFIG_ARCH_K3) += k3-am62x-sk-csi2-imx219.dtbo
>   dtb-$(CONFIG_ARCH_K3) += k3-am62x-sk-hdmi-audio.dtbo
> +dtb-$(CONFIG_ARCH_K3) += k3-am62x-sk-dss-shared-mode.dtbo
>   
>   # Boards with AM64x SoC
>   dtb-$(CONFIG_ARCH_K3) += k3-am642-evm.dtb
> diff --git a/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi b/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi
> index 33768c02d8eb..8b55ca10102f 100644
> --- a/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi
> +++ b/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi
> @@ -34,7 +34,7 @@ memory@...00000 {
>   		reg = <0x00000000 0x80000000 0x00000000 0x80000000>;
>   	};
>   
> -	reserved-memory {
> +	reserved_memory: reserved-memory {
>   		#address-cells = <2>;
>   		#size-cells = <2>;
>   		ranges;
> diff --git a/arch/arm64/boot/dts/ti/k3-am62x-sk-dss-shared-mode.dtso b/arch/arm64/boot/dts/ti/k3-am62x-sk-dss-shared-mode.dtso
> new file mode 100644
> index 000000000000..02153748a5c2
> --- /dev/null
> +++ b/arch/arm64/boot/dts/ti/k3-am62x-sk-dss-shared-mode.dtso
> @@ -0,0 +1,33 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/**
> + * DT overlay to enable display sharing mode for AM62P DSS0
> + * This is compatible with custom AM62 Device Manager firmware
> + *
> + * Copyright (C) 2023 Texas Instruments Incorporated - http://www.ti.com/
> + */
> +
> +/dts-v1/;
> +/plugin/;
> +
> +#include <dt-bindings/interrupt-controller/irq.h>
> +#include <dt-bindings/interrupt-controller/arm-gic.h>
> +
> +&dss0 {
> +	ti,dss-shared-mode;
> +	ti,dss-shared-mode-vp = "vp1";
> +	ti,dss-shared-mode-vp-owned = <0>;
> +	ti,dss-shared-mode-common = "common1";
> +	ti,dss-shared-mode-planes = "vid";
> +	ti,dss-shared-mode-plane-zorder = <0>;
> +	interrupts = <GIC_SPI 85 IRQ_TYPE_LEVEL_HIGH>;
> +};
> +
> +&reserved_memory {
> +	#address-cells = <2>;
> +	#size-cells = <2>;
> +	rtos_framebuffer_memory_region: rtos-framebuffer-memory@...00000 {
> +		compatible = "shared-dma-pool";
> +		reg = <0x00 0x94800000 0x00 0x08000000>;
> +		no-map;
> +	};
> +};