linux-kernel - Re: [PATCH AUTOSEL 4.14 086/105] PCI / ACPI: Use cached ACPI device state to get PCI device power state

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Message-ID: <20190722004054.GF1607@sasha-vm>
Date:   Sun, 21 Jul 2019 20:40:54 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.14 086/105] PCI / ACPI: Use cached ACPI device
 state to get PCI device power state

On Tue, Jul 16, 2019 at 11:22:44AM +0200, Rafael J. Wysocki wrote:
>On 7/15/2019 4:28 PM, Sasha Levin wrote:
>>From: Mika Westerberg <mika.westerberg@...ux.intel.com>
>>
>>[ Upstream commit 83a16e3f6d70da99896c7a2639c0b60fff13afb8 ]
>>
>>The ACPI power state returned by acpi_device_get_power() may depend on
>>the configuration of ACPI power resources in the system which may change
>>any time after acpi_device_get_power() has returned, unless the
>>reference counters of the ACPI power resources in question are set to
>>prevent that from happening. Thus it is invalid to use acpi_device_get_power()
>>in acpi_pci_get_power_state() the way it is done now and the value of
>>the ->power.state field in the corresponding struct acpi_device objects
>>(which reflects the ACPI power resources reference counting, among other
>>things) should be used instead.
>>
>>As an example where this becomes an issue is Intel Ice Lake where the
>>Thunderbolt controller (NHI), two PCIe root ports (RP0 and RP1) and xHCI
>>all share the same power resources. The following picture with power
>>resources marked with [] shows the topology:
>>
>>   Host bridge
>>     |
>>     +- RP0 ---\
>>     +- RP1 ---|--+--> [TBT]
>>     +- NHI --/   |
>>     |            |
>>     |            v
>>     +- xHCI --> [D3C]
>>
>>Here TBT and D3C are the shared ACPI power resources. ACPI _PR3() method
>>of the devices in question returns either TBT or D3C or both.
>>
>>Say we runtime suspend first the root ports RP0 and RP1, then NHI. Now
>>since the TBT power resource is still on when the root ports are runtime
>>suspended their dev->current_state is set to D3hot. When NHI is runtime
>>suspended TBT is finally turned off but state of the root ports remain
>>to be D3hot. Now when the xHCI is runtime suspended D3C gets also turned
>>off. PCI core thus has power states of these devices cached in their
>>dev->current_state as follows:
>>
>>   RP0 -> D3hot
>>   RP1 -> D3hot
>>   NHI -> D3cold
>>   xHCI -> D3cold
>>
>>If the user now runs lspci for instance, the result is all 1's like in
>>the below output (00:07.0 is the first root port, RP0):
>>
>>00:07.0 PCI bridge: Intel Corporation Device 8a1d (rev ff) (prog-if ff)
>>     !!! Unknown header type 7f
>>     Kernel driver in use: pcieport
>>
>>In short the hardware state is not in sync with the software state
>>anymore. The exact same thing happens with the PME polling thread which
>>ends up bringing the root ports back into D0 after they are runtime
>>suspended.
>>
>>For this reason, modify acpi_pci_get_power_state() so that it uses the
>>ACPI device power state that was cached by the ACPI core. This makes the
>>PCI device power state match the ACPI device power state regardless of
>>state of the shared power resources which may still be on at this point.
>>
>>Link: https://lore.kernel.org/r/20190618161858.77834-2-mika.westerberg@linux.intel.com
>>Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
>>Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>Signed-off-by: Sasha Levin <sashal@...nel.org>
>>---
>>  drivers/pci/pci-acpi.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>>diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
>>index a3cedf8de863..688e195e85b4 100644
>>--- a/drivers/pci/pci-acpi.c
>>+++ b/drivers/pci/pci-acpi.c
>>@@ -563,7 +563,8 @@ static pci_power_t acpi_pci_get_power_state(struct pci_dev *dev)
>>  	if (!adev || !acpi_device_power_manageable(adev))
>>  		return PCI_UNKNOWN;
>>-	if (acpi_device_get_power(adev, &state) || state == ACPI_STATE_UNKNOWN)
>>+	state = adev->power.state;
>>+	if (state == ACPI_STATE_UNKNOWN)
>>  		return PCI_UNKNOWN;
>>  	return state_conv[state];
>
>This requires additional changes to really work in all cases, please 
>do not include it alone into -stable.

I've dropped it, thanks!

--
Thanks,
Sasha