[OT] Kernel device tree question

[OT] Kernel device tree question

[Gary Thomas]

I know this is a bit off-topic but now that the FSL based
boards are all going to device trees, I thought I might find
my answer quicker here :-)

I have a board (i.MX53) that I need to adjust one of the main
clocks (CKO1).  The default setting uses the main CPU clock
and I need to change it to use one of the PLL based clocks.
I can see where this selector is available as cko1_sel, but
it's not clear to me if/where/how I can set this to be pll3_sw
in the device tree (which in the modern world is the only place
for target platform configuration and control).

Any ideas or pointers?

Thanks

-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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Re: [OT] Kernel device tree question

[Alexandre Belloni]

Hi,

On 24/07/2014 at 08:42:45 -0600, Gary Thomas wrote :
> I have a board (i.MX53) that I need to adjust one of the main
> clocks (CKO1).  The default setting uses the main CPU clock
> and I need to change it to use one of the PLL based clocks.
> I can see where this selector is available as cko1_sel, but
> it's not clear to me if/where/how I can set this to be pll3_sw
> in the device tree (which in the modern world is the only place
> for target platform configuration and control).

Actually, this is exactly what DT is not supposed to be used for. The
device tree must only describe the hardware and the configuration must
be avoided.

> 
> Any ideas or pointers?
> 

cko1_sel seems to be declared correctly as a mux so pll3_sw should be
selected automatically when you need it, by setting ck01.


-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Re: [OT] Kernel device tree question

[Gary Thomas]

On 2014-07-24 09:13, Alexandre Belloni wrote:
> Hi,
>
> On 24/07/2014 at 08:42:45 -0600, Gary Thomas wrote :
>> I have a board (i.MX53) that I need to adjust one of the main
>> clocks (CKO1).  The default setting uses the main CPU clock
>> and I need to change it to use one of the PLL based clocks.
>> I can see where this selector is available as cko1_sel, but
>> it's not clear to me if/where/how I can set this to be pll3_sw
>> in the device tree (which in the modern world is the only place
>> for target platform configuration and control).
>
> Actually, this is exactly what DT is not supposed to be used for. The
> device tree must only describe the hardware and the configuration must
> be avoided.
>
>>
>> Any ideas or pointers?
>>
>
> cko1_sel seems to be declared correctly as a mux so pll3_sw should be
> selected automatically when you need it, by setting ck01.

How/where can I do this?  As I understand it, the only place I can make
such a setup is in the device tree file as that's the only thing unique
for my board.

Thanks

-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
------------------------------------------------------------