Re: [linux-pm] [PATCH] PowerOP, PowerOP Core, 1/2

From: Matthew Locke
Date: Tue Sep 26 2006 - 17:46:18 EST

On Sep 22, 2006, at 7:09 AM, Pavel Machek wrote:


| > >>+struct powerop_driver {
| > >>+ char *name;
| > >>+ void *(*create_point) (const char *pwr_params, va_list args);
| > >>+ int (*set_point) (void *md_opt);
| > >>+ int (*get_point) (void *md_opt, const char *pwr_params, va_list
| > >>args);
| > >>+};
| > >
| > >We can certainly get better interface than va_list, right?
| >
| > Please elaborate.
| va_list does not provide adequate type checking. I do not think it
| suitable in driver<->core interface.

Well, in this particular case the typing probably has to be weak, one
way or another. The meaning of the parameters is arguably opaque at

Why not have struct powerop_parameters, defined in machine-specific
header somewhere, but used everywhere?

We started out with a machine-specific header. The general feedback on the linux-pm list was that a complete machine independent interface was preferred. At first Eugeny and I were against that but the resulting interface is much more flexible. Users of the PowerOP API do not have to include an asm/powerop.h to use it. Instead you can get all the information you need from the interface. Also, using the current implementation you can get/set any arbitrary number and order of the power parameters. For example, a platform has parameters p0-p5. An operating point could be registered with values for p0,p1 and another with p0,p1,p2,p3,p4 and p5. The code that registers operating points and accesses existing operating points don't have to know the correct order of parameters, provide values for the entire parameter list or have a machine specific header. In addition to being machine independent, the current implementation seems to works nicely for integrating with cpufreq.

We are not completely satisfied with the string parsing that results from the current interface but we can improve it over time.

the interface - the attributes may be meaningful to specific components
of the system, but are not defined in the standardized interface (which
would otherwise have to know about all possible kinds of power
attributes and be changed every time a new one is added).

So, if you'd rather have an array of char* or void* values, that would
probably also meet the need, but my guess is that the typing is
intentionally opaque.

Actually array of integers would be better than this.

| > >How is it going to work on 8cpu box? will
| > >you have states like cpu1_800MHz_cpu2_1600MHz_cpu3_800MHz_... ?
| >
| > i do not operate with term 'state' so I don't understand what it means here.
| Okay, state here means "operating point". How will operating points
| look on 8cpu box? That's 256 states if cpus only support "low" and
| "high". How do you name them?

I don't think you would name the compounded states. Each CPU would need
to have its own defined set of operating points (since the capabilities
of the CPUs can reasonably be different).

Well, having few "powerop domains" per system would likely solve that
problem... and problem of 20 devices on my PC. Can we get that?

(cesky, pictures)
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