Re: Shutting down PCI devices on suspend

[Pavel Machek <pavel-+ZI9xUNit7I@public.gmane.org>]

Hi!

> Because the power management design should be layered:
> 
> device power off request -->
> 
> (start)
> |
> | class - disable user space interfaces, stop timers etc
> |
> | driver - save hardware state, prepare hardware for poweroff
> |
> | bus - power off physical device
> |
> | firmware (ex ACPI) - additional power logic (ex external device components
> |					       may need to be powered off.
> |					       This will typically involve Dx
> |					       states)
> /
> (finish)

Driver needs to be in control. For every rule, there's exception
(buggy hw?). It is fine if classes or buses provide helpers, but
ultimately it needs to be driver's suspend using those helpers.

> | driver (*suspend) - tell class to stop logical device (often large amounts
> |		      of duplicate code between drivers)

Well, then feel free to move that duplicate code into helper
functions. I do think that I'd notice that large amounts of duplicate
code, but feel free to prove me wrong.

> |		    - totally ignore ACPI firmware Dx states (how could we
> |		      handle them, we don't know enough about the layers below
> |		      us.  ACPI may not be compiled into the kernel, the device
> |		      may not have ACPI extensions etc.)

Helpers can do that, right?

> > Saving/restoring state is way more work than actual power state
> > transitions. Provide nice helpers so that power state transitions are
> > easy, but leave the work on the drivers, so that drivers may do
> > something special if required.
> 
> Could you provide an example of a special case?  I'm not sure if we should
> design our model around the least common denominator of standard
> compliance.

Well, if you want your network card to do wake-on-lan, you need to
keep it powered on... And the driver is the piece of code that knows
if you want to do wake-on-lan, right?

								Pavel
-- 
People were complaining that M$ turns users into beta-testers...
...jr ghea gurz vagb qrirybcref, naq gurl frrz gb yvxr vg gung jnl!


-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now. 
http://productguide.itmanagersjournal.com/