PXA 2xx devictree port and clock infrastructure

[arnd@arndb.de (Arnd Bergmann)]

On Tuesday 27 May 2014, Robert Jarzmik wrote:
> I'm playing with devicetree to port the mioa701 machine code to devicetree (or
> rather to eliminate the mioa701 machine code).
> 
> While porting the pxa2xx device drivers, I came to a question about the clock
> infrastructure, and I'd need a bit of guidance.
> 
> Many drivers, in their probe code are doing something like :
>         1) regs = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>         2) irq = platform_get_irq(pdev, 0);
>         3) clk = clk_get(&pdev->dev, NULL);
> 
> Points 1 and 2 are straightforward with DT. Point 3 is not so obvious to me.
> 
> As there is no platform data anymore, the clock infrastructure wants to match
> the OF device (in my case udc at 40600000) with the registered
> clocks. Unfortunately, the registered clock is named "pxa27x-udc", which works
> well in "platform data" devices, but not in devicetree populated devices.
> 
> Therefore, I'd like to know what to do, and an example in another platform would
> be great. Should I create a clkdev driver in drivers/clk, or is there another
> ... faster way ? And Daniel, you probably solved it already for
> arch/arm/mach-pxa/pxa-dt.c, didn't you ?

There are generally three ways of doing this:

a) use an auxdata table to reassign the device names to what they
   used to be
b) change the clkdev lookup to also include the new names (e.g. "40600000.udc")
c) write a DT-aware clock driver and list all clocks in DT

	Arnd