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

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Date:	Fri, 20 Jun 2014 15:02:43 -0400
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Arnd Bergmann <arnd@...db.de>, Rob Herring <robherring2@...il.com>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Russell King <linux@....linux.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	Fabio Estevam <festevam@...il.com>,
	Shawn Guo <shawn.guo@...escale.com>
Subject: Re: [PATCH] dt/documentation: add specification of dma bus information

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@...0000 {
>>>> +                               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.

Example:
soc {
		compatible = "ti,keystone","simple-bus";
		ranges = <0x0 0x0 0x0 0xc0000000>;
		dma-ranges = <0x80000000 0x8 0x00000000 0x80000000>;

		[...]

		usb: usb@...0000 {
			compatible = "ti,keystone-dwc3";

			[...]
			dma-coherent;
		};
};

Regards,
Santosh
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