Re: broken bm_sts on 82801CA?

[Nate Lawson <nate-Y6VGUYTwhu0@public.gmane.org>]

On Wed, 8 Oct 2003, Ducrot Bruno wrote:
> On Wed, Oct 08, 2003 at 09:55:35AM -0700, Nate Lawson wrote:
> > On Wed, 8 Oct 2003, Ducrot Bruno wrote:
> > > That more an hardware design issue due to how hotplug work in usb busses
> > > in general, and it may need to be workaround, so if anybody haven't yet worked on
> > > C-states on FreeBSD..  Please note also that Linux do not workaround that
> > > btw.
> >
> > I have implemented C-states in freebsd, that's how I ran into this
> > problem.  I'll be committing the code once it's cleaned up a little.
> >
> > Since Linux always demotes to "don't enter a Cx state" if bm_sts indicates
> > activity, are you saying that if you have a USB bus configured in Linux,
> > you don't even use C1 (HLT)?
>
> What?  If so, there is a bug somewhere since we should look at bm status only at
> C2 (only if we have to go to C3) or C3 state.
> Sound like you are right, btw.  I have to look a little deeper.  Thanks for pointing
> this.

This is from 2.5.74.  If C3 is supported by the platform, unconditionally
set flags.bm_check:

		else {
			pr->power.states[ACPI_STATE_C3].valid = 1;
			pr->power.states[ACPI_STATE_C3].latency_ticks =
				US_TO_PM_TIMER_TICKS(acpi_fadt.plvl3_lat);
			pr->flags.bm_check = 1;
		}

In acpi_processor_idle(), if bm_check, read the bm_sts register and if it
is non-zero, set next_state to be the demotion state but don't sleep this
quantum.  Instead, enable IRQs and stay active:

		if (pr->power.bm_activity & cx->demotion.threshold.bm) {
			local_irq_enable();
			next_state = cx->demotion.state;
			goto end;
		}

However, since this code is run every time acpi_processor_idle() is
called, it will never enter even C2 if you have a bm_sts bit that is
always 1.

-Nate


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