From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH] ACPI / PM: Fix potential problem in acpi_device_get_power() Date: Mon, 25 Mar 2013 14:03:22 +0100 Message-ID: <2098772.7Ti64jKWB7@vostro.rjw.lan> References: <6380949.vJPdL9PvJh@vostro.rjw.lan> <5150045F.2000105@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <5150045F.2000105@intel.com> Sender: linux-pm-owner@vger.kernel.org To: Aaron Lu Cc: ACPI Devel Maling List , Linux PM list , LKML , Len Brown List-Id: linux-acpi@vger.kernel.org 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 > > > > 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. > 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 > > --- > > 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; > > } > > > > /* > > > -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.