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

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