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

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Date:	Fri, 20 Jun 2014 14:46:17 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<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 Fri, Jun 20, 2014 at 2:02 PM, Santosh Shilimkar
<santosh.shilimkar@...com> 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@...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.

Yes. Looks fine.

Rob

>
> 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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