Re: [Dynamicpower-devel] DPM review

[Todd P. <tp...@mv...>]

Livio Tenze wrote:
...
> I read some articles and part of montavista documentation, but some 
> subjects are not clear: in particular I do not understand how the DPM 
> changes the operationg point. I am working on a freescale MX21 

In addition to Matthew's overall explanation (and he's one of the 
original DPM designers, I'm just a johnny-come-lately), some specifics 
about your situation.  MX21 is not currently a part of the 2.6 patches 
maintained here at sourceforge.  You may have MontaVista's 2.4-based 
product and may therefore have access to support channels that can help 
with board specifics.

> Is it mandatory to set the the device constraints?

Are you asking whether you can get away with ignoring the device 
constraints and set whatever operating points you want?  If so, it 
depends on the board-specific behavior of the affected devices, and I 
don't know MX21 well enough to say, but I do know various MX21 drivers 
place lower bounds on HCLK.  Assuming the device constraints are 
properly set up, the effect of setting clocks sourced by those devices 
outside the constrained range might be to wedge the device until the 
next power cycle, or may cause the device to fail to function properly 
until the clocks are put back into the range needed, or might be 
undefined.

-- 
Todd