linux-kernel - Re: [PATCH v1 1/2] PCI: PM: Avoid leaving devices in D0-uninitialized in pci_power

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Message-ID: <YkwRjI0KvpmiJjvK@lahna>
Date:   Tue, 5 Apr 2022 12:53:16 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PCI <linux-pci@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>
Subject: Re: [PATCH v1 1/2] PCI: PM: Avoid leaving devices in
 D0-uninitialized in pci_power_up()

On Mon, Apr 04, 2022 at 05:41:13PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> In theory, pci_power_up() may leave a device in D0-uninitialized
> during a transition from D3cold to D0.
> 
> Say, a PCIe device depending on some ACPI power resources is put into
> D3cold, so the power resources in question are all turned off.  Then,
> pci_power_up() is called to put it into D0.
> 
> It first calls pci_platform_power_transition() which invokes
> platform_pci_set_power_state() to turn on the ACPI power resources
> depended on by the device and, if that is successful, it calls
> pci_update_current_state() to update the current_state field of
> the PCI device object.  If the device's configuration space is
> accessible at this point, which is the case if
> platform_pci_set_power_state() leaves it in D0-uninitialized (and
> there's nothing to prevent it from doing so), current_state will be
> set to PCI_D0 and the pci_raw_set_power_state() called subsequently
> will notice that the device is in D0 already and do nothing.
> However, that is not correct, because it may be still necessary to
> restore the device's BARs at this point.
> 
> To address this issue, set current_state temporarily to PCI_D3hot
> in the cases in which pci_raw_set_power_state() may need to do more
> than just changing the power state of the device.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>