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    SubjectRe: [GIT PULL] DT clk binding support
    On 05/22/2012 08:38 PM, Saravana Kannan wrote:
    > On Tue, May 22, 2012 6:52 am, Rob Herring wrote:
    >> On 05/21/2012 11:17 PM, Stephen Boyd wrote:
    >>> On 05/21/12 19:15, Shawn Guo wrote:
    >>>> On Mon, May 21, 2012 at 06:52:37PM -0500, Rob Herring wrote:
    >>>>> As Grant states: "This proposed binding is only about one thing:
    >>>>> attaching clock providers to clock consumers." This means you have to
    >>>>> have at least a single provider and a single consumer defined in the
    >>>>> DT.
    >>>> I just read through Grant's comments over again. I agree with the
    >>>> statement which implicitly requires the clk provider defined in DT.
    >>>> However, for some case, this provider in DT is just a skeleton which
    >>>> is backed by clock driver where the provider is actually defined.
    >>>> Looking at Grant's comment below, the second option is also to match
    >>>> the clock in driver just using name. The only difference to my
    >>>> proposal is the name here is given by the argument of phandle pointing
    >>>> to that skeleton provider node.
    >>>> I'm fine with that. So go ahead with your bindings.
    >>> Can we do what the regulator framework has done and have a common
    >>> binding of <connection_name>-clk = <&phandle>? Something like:
    >>> core-clk = <&uart3_clk>
    >>> and then have clk_get() use the of node of the device passed in to find
    >>> a property named %s-clk and find the clock with the matching phandle.
    >> Sigh... That is what we had in previous versions from over a year ago
    >> and we moved away from that approach. The current binding has been
    >> reviewed multiple times in the last 6 months...
    >> The current approach is aligned with how interrupts are handled (with
    >> the addition of a phandle). I think not having per clock property names
    >> is easier to parse and easier to document.
    >>> This looks like it's trying to cover both the end consumers (uart uses
    >>> uart3_clk) and the internal clock tree consumers (a crystal oscillator
    >>> connects to a PLL or a mux has multiple parents). We can certainly use
    >>> these bindings for muxes and internal parent-child relationships but I
    >>> would prefer we use different bindings for consumer bindings that match
    >>> what regulators do today.
    >> The binding supports either defining every last internal clock or just
    >> the leaf clocks. I took the former route on highbank since I don't have
    >> a lot of clocks. If I was doing imx or omap for example, I'd probably
    >> just define all the clock controller outputs.
    > If only the leaf nodes are defined in DT, then how is the clock platform
    > driver implementer supposed to instantiate the rest of the tree and
    > connect it up with the partial list of clocks in DT? So, they have to
    > switch back and forth between DT and the .c file which defines the rest
    > and make sure the parent<->child names match?
    > To me it looks that it might better to decouple the description of the
    > clock HW from the mapping of a clock leaf to a consumer device. If we just
    > use a string to identify the clock that's consumed by a device, we can
    > achieve this decoupling at a clean boundary -- clock consumers devices
    > (UART) vs clock producer devices (clock controller in the SoC, in a PMIC,
    > audio codec, etc).
    > With the decoupling, we don't have the inconsistency of having some of the
    > clocks of a clock producer device incompletely defined in DT and the rest
    > of the clocks of the same clock producer device hard coded in the kernel.
    > So, you either put your entire clock tree in the SoC in the DT or put all
    > of it in the kernel but you aren't forced to put just some of them in the
    > DT just to get DT working. I see no benefit in defining only some of the
    > clocks in DT -- it just adds more confusion in the clock tree definition.
    > What am I missing?

    I fail to see what would need changing in the binding itself. The
    binding just describes connections. Whether that is a connection to a
    clock controller node to a device or a clock gate/mux/divider node to a
    device is really beyond the clock binding. This is really just policy.
    You are free to put no clocks in DT, all clocks, or a nexus of clocks.


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