linux-kernel - Re: Point-to-point bus in device tree

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Message-ID: <4F7DF142.5050601@wwwdotorg.org>
Date:	Thu, 05 Apr 2012 13:23:46 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	David Brown <davidb@...eaurora.org>
CC:	devicetree-discuss@...ts.ozlabs.org, linux-arm-msm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: Point-to-point bus in device tree

On 04/05/2012 12:15 PM, David Brown wrote:
> Some MSM SoCs have a small serial-type "bus" that is used to
> communicate with the PMIC devices.  This interface is always
> point-to-point.  I'm doing a device-tree conversion of the driver that
> Ken Heitke posted last year <https://lkml.org/lkml/2011/2/17/503>.
> 
> A naive conversion to device tree, would result in something like
> this:
> 
> 	qcom,ssbi@...000 {
> 		compatible = "qcom,ssbi";
> 		reg = <0x500000 0x1000>;
> 		qcom,controller-type = "ssbi";
> 
> 		qcom,pmic8058@0 {
> 			reg = <0x0 0x01>;
> 			...
> 		}
> 	}
> 
> There would end up being an extraneous register for the device on the
> other end (there are no addresses), and there would need to be code in
> the ssbi driver to traverse this small tree to find these nodes.

Isn't that extra code simply:

of_platform_populate(pdev->dev.of_node, NULL, NULL, &pdev->dev);

That seems like pretty low overhead.
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