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    SubjectRe: Point-to-point bus in device tree
    Date
    On Fri, 6 Apr 2012 08:16:10 -0700, David Brown <davidb@codeaurora.org> wrote:
    > On Thu, Apr 05, 2012 at 01:08:29PM -0700, David Brown wrote:
    > > On Thu, Apr 05, 2012 at 01:23:46PM -0600, Stephen Warren wrote:
    > > > 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@500000 {
    > > > > 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.
    > >
    > > True, but it still bothers me to have to have a bogus register.
    >
    > Ok, not sure where I got that idea, but I don't appear to actually
    > need a register in the pmic8058 node for of_platform_populate to
    > create a platform device. It only needs a compatible field. So, it
    > look like that matches just what I need.

    Correct. Don't use a reg and all will look good.

    g.


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