netdev - Re: [PATCH] [v2] netdev/phy: add MDIO bus multiplexer driven by a memory-mapped device

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Date:	Fri, 24 Aug 2012 13:43:04 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Timur Tabi <timur@...escale.com>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Fleming Andy-AFLEMING <afleming@...escale.com>,
	David Miller <davem@...emloft.net>,
	"ddaney.cavm@...il.com" <ddaney.cavm@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>
Subject: Re: [PATCH] [v2] netdev/phy: add MDIO bus multiplexer driven by a
 memory-mapped device

On 08/24/2012 01:36 PM, Timur Tabi wrote:
> Stephen Warren wrote:
>> When translating the child node's reg property into the parent's address
>> space, the parent's reg property shouldn't even be used at all; all the
>> mapping is done through the ranges property.
>>
>> I thought the code error-checked for a missing ranges property, but I
>> guess not...
> 
> I don't think 'ranges' is always necessary, because sometimes the child
> nodes have a different address space that's not mapped to the parent.  For
> instance, I2C devices have addresses that are not mapped to the I2C
> controller itself.
> 
> Anyway, thanks to Scott for helping me figure this out.  I was missing a
> ranges property:
> 
> 	fpga: board-control@3,0 {
> 		#address-cells = <1>;
> 		#size-cells = <1>;
> 		compatible = "fsl,p5020ds-fpga", "fsl,fpga-ngpixis";
> 		reg = <3 0 0x30>;
> 		ranges = <0 3 0 0x30>;
> 
> This maps the child address of 0 to the parent address of 3 0.  It seems
> obvious now, but it was driving me crazy.  We've never put child devices
> under our FPGA nodes, so there was no prior use case of a 'ranges'
> property in any of the localbus devices that I could learn from.  Plus,
> this is the first time we're probing directly on a child of a localbus device.

There's ep8248e.dts, not that I'd have expected you to look there. :-)

-Scott


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