[v2,2/2] Documentation: DT: Exynos: Bind SRAM though DT

Commit Message

Sachin Kamat May 2, 2014, 5:06 a.m. UTC

Add SRAM binding documentation.

Signed-off-by: Sachin Kamat <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
---
Changes since v1:
Minor re-wording for better clarity.
---
 .../devicetree/bindings/arm/exynos/smp-sram.txt    |   38 ++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/arm/exynos/smp-sram.txt

Comments

Arnd Bergmann May 2, 2014, 8:53 a.m. UTC | #1

On Friday 02 May 2014 10:36:20 Sachin Kamat wrote:
> +       sram@02020000 {
> +               compatible = "mmio-sram";
> +               reg = <0x02020000 0x54000>;
> +               #address-cells = <1>;
> +               #size-cells = <1>;
> +               ranges = <0 0x02020000 0x54000>;
> +

That is actually quite a lot of unused SRAM. Since it came up this
morning in another thread, there may be value in using this for
coherent DMA allocations for some devices. Not sure about how
to best hook this up, but there could be some serious performance
improvements. A typical case would be DMA descriptors for a
gigabit ethernet adapter, which are a pain to maintain on platforms
without cache-coherent DMA.

You could check what drivers you have that call dma_alloc_coherent,
and see if any of them are performance-critical, then hack them
up to use this memory instead as an experiment.

	Arnd

Patch

diff --git a/Documentation/devicetree/bindings/arm/exynos/smp-sram.txt b/Documentation/devicetree/bindings/arm/exynos/smp-sram.txt
new file mode 100644
index 000000000000..c9ff2f58f9b6
--- /dev/null
+++ b/Documentation/devicetree/bindings/arm/exynos/smp-sram.txt
@@ -0,0 +1,38 @@ 
+Samsung Exynos SRAM for SMP bringup:
+------------------------------------
+
+Samsung SMP-capable Exynos SoCs use part of the SRAM for the bringup
+of the secondary cores. Once the core gets powered up it executes the
+code that is residing at some specific location of the SRAM.
+
+Therefore reserved section sub-nodes have to be added to the mmio-sram
+declaration. These nodes are of two types depending upon secure or
+non-secure execution environment.
+
+Required sub-node properties:
+- compatible : depending upon boot mode, should be
+		"samsung,exynos4210-sram" : for Secure SYSRAM
+		"samsung,exynos4210-sram-ns" : for Non-secure SYSRAM
+
+The rest of the properties should follow the generic mmio-sram discription
+found in ../../misc/sram.txt
+
+Example:
+
+	sram@02020000 {
+		compatible = "mmio-sram";
+		reg = <0x02020000 0x54000>;
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges = <0 0x02020000 0x54000>;
+
+		smp-sram@0 {
+			compatible = "samsung,exynos4210-sram";
+			reg = <0x0 0x1000>;
+		};
+
+		smp-sram@53000 {
+			compatible = "samsung,exynos4210-sram-ns";
+			reg = <0x53000 0x1000>;
+		};
+	};