Re: PowerOp Design and working patch

[Tim Bird <tim.bird@am.sony.com>]

david singleton wrote:
> On Aug 1, 2006, at 3:09 AM, Matthew Locke wrote:
>>Well, no one is suggesting a user define and install that info.  
>>Operating point creation will be done by someone who understands the 
>>system (system designer) regardless of the method used to get the 
>>operating points in the kernel.
> 
> It sounds to me like they don't want to have to change kernel code and 
> recompile the kernel
> to get a new operating point.
> 
> It sounds like they are talking about a dynamic operating point as a 
> loadable
> module, which would fit perfectly with the PowerOp scheme, since it's 
> the
> system designer who would be creating the new  dynamic operating point,
> not the user.

Often, in the embedded world, the person defining the operating
states will not be a kernel developer, and may not be comfortable
with, or capable of, creating a kernel module.  (There are
significant sections of the embedded space where modules are
not used at all, and no module support is compiled into the
kernel.)  In these cases, requiring loadable module support
for runtime OPs would be a problem.

> 
> The point of PowerOp is that the system designer creates (and validates)
> the operating points that the hardware vendor supports, not the user.
> 
> A system designer creating a new operating point as a loadable
> module would satisfy this requirement, and the user would not
> be able to put the system into an undefined state, either by accident
> or maliciously.
>

OK, I think I understand better your objection to user-space
created operating points.   In embedded projects, it is often
assumed that no one but the system designer has access to
arbitrary user space programs.  Hence, it sometimes doesn't
register that an end user could or would utilize a particular
interface, just because it existed.

Would not the normal Unix permissions system prevent the
"bad state" problem, in the non-embedded case?

  -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Electronics
=============================