Re: [PATCH v3 2/2] ARM: dts: tegra20: Add video decoder node

[Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>]

Hello Dmitry,

On 10/11/2017 11:08 PM, Dmitry Osipenko wrote:
> Add a device node for the video decoder engine found on Tegra20.
> 
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
>  arch/arm/boot/dts/tegra20.dtsi | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/arch/arm/boot/dts/tegra20.dtsi b/arch/arm/boot/dts/tegra20.dtsi
> index 7c85f97f72ea..1b5d54b6c0cb 100644
> --- a/arch/arm/boot/dts/tegra20.dtsi
> +++ b/arch/arm/boot/dts/tegra20.dtsi
> @@ -249,6 +249,23 @@
>  		*/
>  	};
>  
> +	vde@6001a000 {
> +		compatible = "nvidia,tegra20-vde";
> +		reg = <0x6001a000 0x3D00    /* VDE registers */
> +		       0x40000400 0x3FC00>; /* IRAM region */

this notation of a used region in IRAM is non-standard and potentially it
may lead to conflicts for IRAM resource between users.

My proposal is to add a valid device tree node to describe an IRAM region
firstly, then reserve a subregion in it by using a new "iram" property.

----8<----
From: Vladimir Zapolskiy <vz@mleia.com>
Date: Thu, 12 Oct 2017 10:25:45 +0300
Subject: [PATCH] ARM: tegra: add device tree node to describe IRAM on Tegra20

All Tegra20 SoCs contain 256KiB IRAM, which is used to store
resume code and by a video decoder engine.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
---
 arch/arm/boot/dts/tegra20.dtsi | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm/boot/dts/tegra20.dtsi b/arch/arm/boot/dts/tegra20.dtsi
index 7c85f97f72ea..fd2843c90920 100644
--- a/arch/arm/boot/dts/tegra20.dtsi
+++ b/arch/arm/boot/dts/tegra20.dtsi
@@ -9,6 +9,14 @@
 	compatible = "nvidia,tegra20";
 	interrupt-parent = <&lic>;
 
+	iram@40000000 {
+		compatible = "mmio-sram";
+		reg = <0x40000000 0x40000>;
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges = <0 0x40000000 0x40000>;
+	};
+
 	host1x@50000000 {
 		compatible = "nvidia,tegra20-host1x", "simple-bus";
 		reg = <0x50000000 0x00024000>;
----8<----

Please add the change above to your next version of the series, or
if you wish I can send it separately for review by Thierry.

After applying that change you do define a region in IRAM for the exclusive
usage by a video decoder engine and add an 'iram' property:

----8<----
diff --git a/arch/arm/boot/dts/tegra20.dtsi b/arch/arm/boot/dts/tegra20.dtsi
index fd2843c90920..5133fbac2185 100644
--- a/arch/arm/boot/dts/tegra20.dtsi
+++ b/arch/arm/boot/dts/tegra20.dtsi
@@ -15,6 +15,11 @@
 		#address-cells = <1>;
 		#size-cells = <1>;
 		ranges = <0 0x40000000 0x40000>;
+
+		vde_pool: vde {
+			reg = <0x400 0x3fc00>;
+			pool;
+		};
 	};
 
 	host1x@50000000 {
[snip]

+	vde@6001a000 {
+		compatible = "nvidia,tegra20-vde";
+		reg = <0x6001a000 0x3d00>;	/* VDE registers */
+		iram = <&vde_pool>;		/* IRAM region */
[snip]
----8<----

And finally in the driver you'll use genalloc API to access the IRAM
region, for that you can find ready examples in the kernel source code.

--
With best wishes,
Vladimir