From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aaron Lu Subject: Re: [PATCH] ACPI / PM: Fix potential problem in acpi_device_get_power() Date: Mon, 25 Mar 2013 16:01:35 +0800 Message-ID: <5150045F.2000105@intel.com> References: <6380949.vJPdL9PvJh@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mga11.intel.com ([192.55.52.93]:60348 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755726Ab3CYIAW (ORCPT ); Mon, 25 Mar 2013 04:00:22 -0400 In-Reply-To: <6380949.vJPdL9PvJh@vostro.rjw.lan> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Rafael J. Wysocki" Cc: ACPI Devel Maling List , Linux PM list , LKML , Len Brown On 03/24/2013 07:57 AM, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki > > 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 > --- > 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; > } > > /* >