mvebu: tclk detection for armada-xp and marvell packet processor with integrated CPU

[thomas.petazzoni@free-electrons.com (Thomas Petazzoni)]

Dear Chris Packham,

On Mon, 17 Nov 2014 02:12:51 +0000, Chris Packham wrote:

> One of the first problems I encountered looking at the Marvell Packet 
> Processor with integrated CPU (I'll refer to that as 'the PP' throughout 
> the rest of this email) was that it has a different TCLK to the armada-xp.
> 
> It appears that for both the PP and the armada-xp the TCLK is hard-coded 
> (to 200MHz and 250MHz respectively) and cannot be detected as far as I 
> can see from the various data-sheets. I was hoping to re-use 
> drivers/clk/mvebu/armada-xp.c but I need to figure out how to make 
> axp_get_tclk_freq() give me an appropriate answer depending on the SoC. 
> If this were in the mach-mvebu code I could just use mvebu_get_soc_id() 
> to fetch the device id. Is there an equivalent I could use in generic code?
> 
> One option would be to use a different compatible string in the dts. 
> That would also give me a way of handling other differences (the 
> clock-gating is a subset of what's available on the armada-xp). How 
> different would things have to be before it's worth spinning the PP code 
> out into a file of it's own?

To me, it indeed seems like you need a different compatible string
here. Whether a separate file from drivers/clk/mvebu/armada-xp.c is
needed or not will depend on whether only the tclk frequency differs,
or whether also the ratios with other clocks differ.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com