On Wednesday, 7 of May 2008, Alan Stern wrote:
> On Wed, 7 May 2008, Rafael J. Wysocki wrote:
>
> > On Wednesday, 7 of May 2008, Pavel Machek wrote:
> > > Hi!
> > >
> > > > From: Rafael J. Wysocki <rjw@xxxxxxx>
> > > >
> > > > The new suspend and hibernation callbacks introduced with
> > > > 'struct pm_ops' and 'struct pm_ext_ops' do not take a
> > > > pm_message_t argument, so the drivers using them will not be able
> > > > to use pci_choose_state() in its present form. For this reason,
> > > > introduce the new function pci_preferred_state() playing the role
> > > > of pci_choose_state(), but taking only a pointer to the device
> > > > object.
> > > >
> > > > Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
> > > > ---
> > > > drivers/pci/pci.c | 33 ++++++++++++++++++++++++++++++++-
> > > > include/linux/pci.h | 1 +
> > > > include/linux/pm.h | 10 ++++++++++
> > > > 3 files changed, 43 insertions(+), 1 deletion(-)
> > > >
> > > > Index: linux-2.6/drivers/pci/pci.c
> > > > ===================================================================
> > > > --- linux-2.6.orig/drivers/pci/pci.c
> > > > +++ linux-2.6/drivers/pci/pci.c
> > > > @@ -509,7 +509,38 @@ pci_set_power_state(struct pci_dev *dev,
> > > > }
> > > >
> > > > pci_power_t (*platform_pci_choose_state)(struct pci_dev *dev);
> > > > -
> > > > +
> > > > +/**
> > > > + * pci_preferred_state - Choose the preferred power state of a PCI device
> > > > + * @dev: PCI device to be put into the low power state
> > > > + * @sp: Information aboutabout what the driver would prefer to do with
> > > > + * the device if there were no platform-implemeted policy.
> > > > + *
> > > > + * Returns PCI power state suitable for given device and given suspend policy.
> > > > + * The policy, however, is only used if platform_pci_choose_state() fails or is
> > > > + * not present. Otherwise, it is assumed that platform_pci_choose_state()
> > > > + * implements the right policy.
> > > > + */
> > > > +
> > > > +pci_power_t pci_preferred_state(struct pci_dev *dev, enum suspend_policy sp)
> > > > +{
> > > > + pci_power_t ret;
> > > > +
> > > > + if (!pci_find_capability(dev, PCI_CAP_ID_PM))
> > > > + return PCI_D0;
> > > > +
> > > > + ret = (sp == SP_TURN_OFF) ? PCI_D3hot : PCI_D0;
> > > > + if (platform_pci_choose_state) {
> > > > + pci_power_t platform_ret = platform_pci_choose_state(dev);
> > > > +
> > > > + if (platform_ret != PCI_POWER_ERROR)
> > > > + ret = platform_ret;
> > > > + }
> > > > + return ret;
> > > > +}
> > > > +
> > > > +EXPORT_SYMBOL(pci_preferred_state);
> > >
> > > I don't get it. How is driver supposed to use this? How does the
> > > driver decide between SP_TURN_OFF and SP_TURN_ON?
> > >
> > > ...and it seems to be clearer to just inline this in the driver... or
> > > pass PCI_D3hot/PCI_D0 to it, instead of inventing yet another
> > > define...
> >
> > I thought about that too. I'd like to know what the other people think,
> > though.
>
> The point of this isn't at all clear.
>
> Is this routine meant to be called during a hibernation
> transition?
Yes, it is.
> Or is it just for suspend?
>
> And why would the return value ever be anything other than D3_hot? (Or
> why would the driver ever want to put a device in a different state?)
In principle, the driver may want to put the device into a state having shorter
wake up latency than D3_hot.
> AFAICS, the only reason would be because platform_pci_choose_state()
> suggested something else. In which case there's no need for the
> "policy" argument.
There is a need in two cases:
- if platform_pci_choose_state() is not defined (it only is defined for ACPI
systems at the moment),
- if platform_pci_choose_state() returns PCI_POWER_ERROR meaning that it cannot
handle the device.
I agree with Pavel that the driver could pass a "fallback state" as a second
argument to be used in case the platform cannot provide it with one.
Thanks,
Rafael
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