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Date:   Thu, 7 Apr 2022 12:51:07 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc:     Linux ACPI <linux-acpi@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: Re: [PATCH v1 3/3] PCI: ACPI: PM: Power up devices in D3cold before
 scanning them
Message-ID: <20220407175107.GA252647@bhelgaas>
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In-Reply-To: <5729439.MhkbZ0Pkbq@kreacher>
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On Mon, Apr 04, 2022 at 05:25:04PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> The initial configuration of ACPI power resources on some systems
> implies that some PCI devices on them are initially in D3cold.
> 
> In some cases, especially for PCIe Root Ports, this is a "logical"
> D3cold, meaning that the configuration space of the device is
> accessible, but some of its functionality may be missing, but it
> very well may be real D3cold, in which case the device will not
> be accessible at all.  However, the PCI bus type driver will need
> to access its configuration space in order to enumerate it.
> 
> To prevent possible device enumeration failures that may ensue as
> a result of ACPI power resources being initially in the "off"
> state, power up all children of the host bridge ACPI device object
> that hold valid _ADR objects (which indicates that they will be
> enumerated by the PCI bus type driver) and do that to all children
> of the ACPI device objects corresponding to PCI bridges (including
> PCIe ports).
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/acpi/pci_root.c |    2 ++
>  drivers/pci/pci-acpi.c  |    3 +++
>  2 files changed, 5 insertions(+)
> 
> Index: linux-pm/drivers/acpi/pci_root.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/pci_root.c
> +++ linux-pm/drivers/acpi/pci_root.c
> @@ -927,6 +927,8 @@ struct pci_bus *acpi_pci_root_create(str
>  		host_bridge->preserve_config = 1;
>  	ACPI_FREE(obj);
>  
> +	acpi_dev_power_up_children_with_adr(device);
> +
>  	pci_scan_child_bus(bus);
>  	pci_set_host_bridge_release(host_bridge, acpi_pci_root_release_info,
>  				    info);
> Index: linux-pm/drivers/pci/pci-acpi.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-acpi.c
> +++ linux-pm/drivers/pci/pci-acpi.c
> @@ -1374,6 +1374,9 @@ void pci_acpi_setup(struct device *dev,
>  
>  	acpi_pci_wakeup(pci_dev, false);
>  	acpi_device_power_add_dependent(adev, dev);
> +
> +	if (pci_is_bridge(pci_dev))
> +		acpi_dev_power_up_children_with_adr(adev);
>  }
>  
>  void pci_acpi_cleanup(struct device *dev, struct acpi_device *adev)
> 
> 
>