On 03/24/2013 07:57 AM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> 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 agree that, at least from OSPM's perspective, D3hot is better than D0
here.
Thanks,
Aaron
>
> 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 <rafael.j.wysocki@xxxxxxxxx>
> ---
> 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;
> }
>
> /*
>
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