On 03/25/2013 09:03 PM, Rafael J. Wysocki wrote: > On Monday, March 25, 2013 04:01:35 PM Aaron Lu wrote: >> On 03/24/2013 07:57 AM, Rafael J. Wysocki wrote: >>> From: Rafael J. Wysocki <[email protected]> >>> >>> Theoretically, in some situations acpi_device_get_power() may return >>> an incorrect result, because the settings of the power resources >>> depended on by the device may indicate a power state shallower than >>> the actual power state of the device. >>> >>> Say that two devices, A and B, depend on two power resources, X and >>> Y, in such a way that _PR0 for both A and B list both X and Y and >>> _PR3 for both A and B list power resource Y alone. Also suppose >>> that _PS0 and _PS3 are present for both A and B. Then, if devices >>> A and B are initially in D0, power resources X and Y are initially >>> "on" and their reference counters are equal to 2. To put device A >>> into power state D3hot the kernel will decrement the reference >>> counter of power resource X, but that power resource won't be turned >>> off, because it is still in use by device B (its reference counter is >>> equal to 1). Next, _PS3 will be executed for device A. Afterward >>> the configuration of the power resources will indicate that device >>> A is in power state D0 (both X and Y are "on"), but in fact it is >>> in D3hot (because _PS3 has been executed for it). >> >> I'm not sure if D3hot is correct here, since the power resource X is >> still on? > > I believe so. We have followed the procedure to put the device into D3hot. > If _PS3 were not executed, that would be moot, but then arguably _PSC should > not return 3.
OK, please feel free to add my Reviewed-by tag then. Thanks, Aaron > >> I agree that, at least from OSPM's perspective, D3hot is better than D0 >> here. > > Yes, it is. > > Thanks, > Rafael > > >>> In that situation, if acpi_device_get_power() is called to get the >>> power state of device A, it will first execute _PSC for it which >>> should return 3. That will cause acpi_device_get_power() to run >>> acpi_power_get_inferred_state() for device A and the resultant power >>> state will be D0, which is incorrect. >>> >>> To fix that change acpi_device_get_power() to first execute >>> acpi_power_get_inferred_state() for the given device (if it >>> depends on power resources) and to evaluate _PSC for it subsequently, >>> so that the result inferred from the power resources configuration >>> can be amended by the _PSC return value. >>> >>> Signed-off-by: Rafael J. Wysocki <[email protected]> >>> --- >>> drivers/acpi/device_pm.c | 39 ++++++++++++++++++++++++--------------- >>> 1 file changed, 24 insertions(+), 15 deletions(-) >>> >>> Index: linux-pm/drivers/acpi/device_pm.c >>> =================================================================== >>> --- linux-pm.orig/drivers/acpi/device_pm.c >>> +++ linux-pm/drivers/acpi/device_pm.c >>> @@ -145,27 +145,36 @@ int acpi_device_get_power(struct acpi_de >>> } >>> >>> /* >>> - * Get the device's power state either directly (via _PSC) or >>> - * indirectly (via power resources). >>> + * Get the device's power state from power resources settings and _PSC, >>> + * if available. >>> */ >>> + if (device->power.flags.power_resources) { >>> + int error = acpi_power_get_inferred_state(device, &result); >>> + if (error) >>> + return error; >>> + } >>> if (device->power.flags.explicit_get) { >>> + acpi_handle handle = device->handle; >>> unsigned long long psc; >>> - acpi_status status = acpi_evaluate_integer(device->handle, >>> - "_PSC", NULL, &psc); >>> + acpi_status status; >>> + >>> + status = acpi_evaluate_integer(handle, "_PSC", NULL, &psc); >>> if (ACPI_FAILURE(status)) >>> return -ENODEV; >>> >>> - result = psc; >>> - } >>> - /* The test below covers ACPI_STATE_UNKNOWN too. */ >>> - if (result <= ACPI_STATE_D2) { >>> - ; /* Do nothing. */ >>> - } else if (device->power.flags.power_resources) { >>> - int error = acpi_power_get_inferred_state(device, &result); >>> - if (error) >>> - return error; >>> - } else if (result == ACPI_STATE_D3_HOT) { >>> - result = ACPI_STATE_D3; >>> + /* >>> + * The power resources settings may indicate a power state >>> + * shallower than the actual power state of the device. >>> + * >>> + * Moreover, on systems predating ACPI 4.0, if the device >>> + * doesn't depend on any power resources and _PSC returns 3, >>> + * that means "power off". We need to maintain compatibility >>> + * with those systems. >>> + */ >>> + if (psc > result && psc < ACPI_STATE_D3_COLD) >>> + result = psc; >>> + else if (result == ACPI_STATE_UNKNOWN) >>> + result = psc > ACPI_STATE_D2 ? ACPI_STATE_D3_COLD : psc; >>> } >>> >>> /* >>> >> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
