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

Chris Packham Chris.Packham at
Mon Nov 17 12:18:59 PST 2014

Hi Andrew,

On 11/18/2014 03:18 AM, Andrew Lunn wrote:
> On Mon, Nov 17, 2014 at 09:34:37AM +0100, Thomas Petazzoni wrote:
>> 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.
> I agree here about the compatibility string. The Kirkwood PP also has
> a different compat string for some drivers and an .dtsi file.
> kirkwood-98dx4122.dtsi

Off topic but, cool bobcat1 support (err, I mean I recognize that 
official part number).

We have existing products using this and others with a proper kirkwood. 
Unfortunately they all have fdt unaware bootloaders. Is there an arm 
equivalent to the cuboot support that powerpc has?

> 	Andrew

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