Re: [PATCH] dt/documentation: add specification of dma bus information
From: Grygorii Strashko
Date: Fri Sep 19 2014 - 14:30:47 EST
Hi Rob,
On 06/22/2014 10:40 PM, Santosh Shilimkar wrote:
On Friday 20 June 2014 03:46 PM, Rob Herring wrote:
On Fri, Jun 20, 2014 at 2:02 PM, Santosh Shilimkar
<santosh.shilimkar@xxxxxx> wrote:
On Friday 20 June 2014 02:56 PM, Arnd Bergmann wrote:
On Friday 20 June 2014 13:17:43 Santosh Shilimkar wrote:
+ dma-coherent;
+ dma-ranges;
+
+ dwc3@2690000 {
+ compatible = "synopsys,dwc3";
+ [...]
+ };
This example is a bit strange. I don't understand the relationship
between keystone-dwc3 and synopsys,dwc3, nor do I want to. I'd prefer
to see a simple example here.
dma-ranges is a property of the parent which you show, but
dma-coherent originally was a property of the bus master itself. While
we need to support that, are we changing that? We need to be clear on
where the property belongs even if the kernel is more lax.
I don't think we are changing it fundamentally but may be I missing
your point. The dma-coherent as is now a per-device property.
USB is one of the bus master supports coherency and hence showed
up in above example.
I think it's enough if you just drop the "synopsys,dwc3" node and the
intermediate dma-ranges property from the example, leaving the
dma-coherent property in the "ti,keystone-dwc3" node.
Thanks Arnd. That should avoid the confusion. Just to see if Rob is
fine by it, the example will look like below.
Yes. Looks fine.
Great. Updated version 2 below.
Seems, this patch has not been merged accidentally :(
Is it possible for you to take it, or would you like me to re-send it?
From 7df26004fe11b7d3ef9592161205c69e1fb663be Mon Sep 17 00:00:00 2001
From: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
Date: Fri, 20 Jun 2014 11:01:54 -0400
Subject: [PATCH v2] dt/documentation: add specification of dma bus information
Recently we introduced the generic device tree infrastructure for couple of DMA
bus parameter, dma-ranges and dma-coherent. Update the documentation so that
its useful for future users.
The "dma-ranges" property is intended to be used for describing the
configuration of DMA bus RAM addresses and its offset w.r.t CPU addresses.
The "dma-coherent" property is intended to be used for identifying devices
supported coherent DMA operations.
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Grant Likely <grant.likely@xxxxxxxxxx>
Cc: Rob Herring <robh+dt@xxxxxxxxxx>
Cc: Pawel Moll <pawel.moll@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Ian Campbell <ijc+devicetree@xxxxxxxxxxxxxx>
Cc: Kumar Gala <galak@xxxxxxxxxxxxxx>
Acked-by: Shawn Guo <shawn.guo@xxxxxxxxxxxxx>
Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
---
Documentation/devicetree/booting-without-of.txt | 53 +++++++++++++++++++++++
1 file changed, 53 insertions(+)
diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
index 1f013bd..7768518 100644
--- a/Documentation/devicetree/booting-without-of.txt
+++ b/Documentation/devicetree/booting-without-of.txt
@@ -51,6 +51,8 @@ Table of Contents
VIII - Specifying device power management information (sleep property)
+ IX - Specifying dma bus information
+
Appendix A - Sample SOC node for MPC8540
@@ -1332,6 +1334,57 @@ reasonably grouped in this manner, then create a virtual sleep controller
(similar to an interrupt nexus, except that defining a standardized
sleep-map should wait until its necessity is demonstrated).
+IX - Specifying dma bus information
+
+Some devices may have DMA memory range shifted relatively to the beginning of
+RAM, or even placed outside of kernel RAM. For example, the Keystone 2 SoC
+worked in LPAE mode with 4G memory has:
+- RAM range: [0x8 0000 0000, 0x8 FFFF FFFF]
+- DMA range: [ 0x8000 0000, 0xFFFF FFFF]
+and DMA range is aliased into first 2G of RAM in HW.
+
+In such cases, DMA addresses translation should be performed between CPU phys
+and DMA addresses. The "dma-ranges" property is intended to be used
+for describing the configuration of such system in DT.
+
+In addition, each DMA master device on the DMA bus may or may not support
+coherent DMA operations. The "dma-coherent" property is intended to be used
+for identifying devices supported coherent DMA operations in DT.
+
+* DMA Bus master
+Optional property:
+- dma-ranges: <prop-encoded-array> encoded as arbitrary number of triplets of
+ (child-bus-address, parent-bus-address, length). Each triplet specified
+ describes a contiguous DMA address range.
+ The dma-ranges property is used to describe the direct memory access (DMA)
+ structure of a memory-mapped bus whose device tree parent can be accessed
+ from DMA operations originating from the bus. It provides a means of
+ defining a mapping or translation between the physical address space of
+ the bus and the physical address space of the parent of the bus.
+ (for more information see ePAPR specification)
+
+* DMA Bus child
+Optional property:
+- dma-ranges: <empty> value. if present - It means that DMA addresses
+ translation has to be enabled for this device.
+- dma-coherent: Present if dma operations are coherent
+
+Example:
+soc {
+ compatible = "ti,keystone","simple-bus";
+ ranges = <0x0 0x0 0x0 0xc0000000>;
+ dma-ranges = <0x80000000 0x8 0x00000000 0x80000000>;
+
+ [...]
+
+ usb: usb@2680000 {
+ compatible = "ti,keystone-dwc3";
+
+ [...]
+ dma-coherent;
+ };
+};
+
Appendix A - Sample SOC node for MPC8540
========================================
Regards,
-grygorii
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