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

[Rob Herring]

On Fri, Jun 20, 2014 at 10:04 AM, Santosh Shilimkar
<santosh.shilimkar@xxxxxx> wrote:
> On Monday 09 June 2014 09:59 AM, Santosh Shilimkar wrote:
>> On Sunday 08 June 2014 10:13 PM, Fabio Estevam wrote:
>>> On Thu, Jun 5, 2014 at 12:22 PM, Santosh Shilimkar
>>> <santosh.shilimkar@xxxxxx> wrote:
>>>> 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: Shawn Guo <shawn.guo@xxxxxxxxxxxxx>
>>>> Cc: Kumar Gala <galak@xxxxxxxxxxxxxx>
>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
>>>> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
>>>> ---
>>>>  Documentation/devicetree/booting-without-of.txt |   60 +++++++++++++++++++++++
>>>>  1 file changed, 60 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
>>>> index 1f013bd..f0120c1 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)
>>>>
>>>> +  VIV - Specifying dma bus information
>>>
>>> "9" in Roman numeral is "IX"
>>>
>> Yeah.. Not sure what I was thinking...
>>
> Updated patch end of the email with the typo fixed.
>
> Rob,
> Can you please pick this up if you are ok with the it.
>
> Regards,
> Santosh
>
> From b72e949a194d766fe029fe6bb5939467f2fbe9b9 Mon Sep 17 00:00:00 2001
> From: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
> Date: Fri, 20 Jun 2014 11:01:54 -0400
> Subject: [PATCH] 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 |   60 +++++++++++++++++++++++
>  1 file changed, 60 insertions(+)
>
> diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
> index 1f013bd..0b0928c 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 +1334,64 @@ 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;
> +                       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.

Rob
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