Subject: [PATCH] dt/documentation: add specification of dma bus information

From: [email-masked] (Grygorii Strashko)
Date: Fri, 19 Sep 2014 21:29:29 +0300

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
>> <[email-masked]> 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 at 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 <[email-masked]>
> 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 <[email-masked]>
> Cc: Grant Likely <[email-masked]>
> Cc: Rob Herring <[email-masked]>
> Cc: Pawel Moll <[email-masked]>
> Cc: Mark Rutland <[email-masked]>
> Cc: Ian Campbell <[email-masked]>
> Cc: Kumar Gala <[email-masked]>
> Acked-by: Shawn Guo <[email-masked]>
> Signed-off-by: Grygorii Strashko <[email-masked]>
> Signed-off-by: Santosh Shilimkar <[email-masked]>
> ---
>   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 at 2680000 {
> +			compatible = "ti,keystone-dwc3";
> +
> +			[...]
> +			dma-coherent;
> +		};
> +};
> +
>   Appendix A - Sample SOC node for MPC8540
>   ========================================
>
>

Regards,
-grygorii