Messages in this thread | | | Date | Wed, 23 May 2012 08:59:41 -0500 | From | Rob Herring <> | Subject | Re: [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.
Rob
| |