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: <91bafebd-ccbe-d6ea-134d-77c8d9776ac8@ti.com>
Date: Thu, 8 Feb 2024 16:35:27 +0530
From: Devarsh Thakkar <devarsht@...com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.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 Tomi,

Thanks for the review.

On 23/01/24 13:59, Tomi Valkeinen wrote:
> 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?
> 

Well, I think the R5 SPL initializes full DDR before starting firmwares
on remote cores and the regions used by this remote cores be it for IPC
or Code/data are marked as reserved both in Linux as well as U-boot so
that Linux/U-boot does not use it [1].

Same scheme is followed here w.r. t RTOS framebuffer too.

[1] :
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi?h=v6.7#n63

Regards
Devarsh

>  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;
>> +    };
>> +};
> 
>