On Monday 18 May 2009, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rjw@xxxxxxx> > > After attempting to change the power state of a PCI device > pci_raw_set_power_state() doesn't check if the value it wrote into > the device's PCI_PM_CTRL register has been stored in there. Still, > it modifies the device's current_state field as though that's the > case. This may cause the driver of the device to think that its > power state has been changed while in fact it hasn't. > > To prevent such situations from happening modify > pci_raw_set_power_state() so that it reads the device's PCI_PM_CTRL > register after writing into it and uses the value read from the > register to update the device's current_state field. Also make it > return -EIO if the new state of the device is not equal to the state > requested by the called. > > To distinguish this error condition from the other ones make > pci_raw_set_power_state() return -ENOSYS instead of -EIO when it is > impossible to change the power state of the device, because it > doesn't support the native PCI PM at all or the requested target > state is not supported by it. Having reconsidered it I think that -ENODEV is probably better than -ENOSYS for this purpose. Updated patch follows. Thanks, Rafael --- From: Rafael J. Wysocki <rjw@xxxxxxx> Subject: PCI PM: Read device power state from register after updating it After attempting to change the power state of a PCI device pci_raw_set_power_state() doesn't check if the value it wrote into the device's PCI_PM_CTRL register has been stored in there. Still, it modifies the device's current_state field as though that's the case. This may cause the driver of the device to think that its power state has been changed while in fact it hasn't. To prevent such situations from happening modify pci_raw_set_power_state() so that it reads the device's PCI_PM_CTRL register after writing into it and uses the value read from the register to update the device's current_state field. Also make it return -EIO if the new state of the device is not equal to the state requested by the called. To distinguish this error condition from the other ones make pci_raw_set_power_state() return -ENODEV instead of -EIO when it is impossible to change the power state of the device, because it doesn't support the native PCI PM at all or the requested target state is not supported by it. Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx> --- drivers/pci/pci.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) Index: linux-2.6/drivers/pci/pci.c =================================================================== --- linux-2.6.orig/drivers/pci/pci.c +++ linux-2.6/drivers/pci/pci.c @@ -446,7 +446,7 @@ static int pci_raw_set_power_state(struc return 0; if (!dev->pm_cap) - return -EIO; + return -ENODEV; if (state < PCI_D0 || state > PCI_D3hot) return -EINVAL; @@ -465,7 +465,7 @@ static int pci_raw_set_power_state(struc /* check if this device supports the desired state */ if ((state == PCI_D1 && !dev->d1_support) || (state == PCI_D2 && !dev->d2_support)) - return -EIO; + return -ENODEV; pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr); @@ -502,7 +502,11 @@ static int pci_raw_set_power_state(struc else if (state == PCI_D2 || dev->current_state == PCI_D2) udelay(PCI_PM_D2_DELAY); - dev->current_state = state; + pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr); + dev->current_state = (pmcsr & PCI_PM_CTRL_STATE_MASK); + /* Return error code if we have failed to change the state */ + if (dev->current_state != state) + return -EIO; /* According to section 5.4.1 of the "PCI BUS POWER MANAGEMENT * INTERFACE SPECIFICATION, REV. 1.2", a device transitioning -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
