linux-kernel - Re: [PATCH] PCI: fix sriov enabling with virtual bus

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Date:	Wed, 05 Nov 2014 23:42:18 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	linux-acpi@...r.kernel.org, Chao Zhou <chao.zhou@...el.com>,
	Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] PCI: fix sriov enabling with virtual bus

On Wednesday, November 05, 2014 02:57:13 PM Bjorn Helgaas wrote:
> On Wed, Nov 05, 2014 at 10:44:25PM +0100, Rafael J. Wysocki wrote:
> > On Wednesday, November 05, 2014 01:22:52 PM Bjorn Helgaas wrote:
> > > ...
> > > The acpi_pci_get_bridge_handle(struct pci_bus *) interface niggles at me a
> > > little because I don't think there's any concept of an ACPI device for a
> > > PCI *bus*, so it doesn't seem like a very good fit to say "find the handle
> > > for this bus".  But that's for later.
> > 
> > To me it does what it says: Get me the handle of the bridge leading to
> > this bus.
> 
> Yeah, I know, it's a great name because it does *exactly* what the name
> says.  I'm just wondering if there's a nicer way to express what the caller
> needs.
> 
> Two of the three callers start with a pci_dev, look up a pci_bus to pass
> in, and get back a handle corresponding to a pci_host_bridge or a pci_dev
> (or a NULL).  It seems a little cluttered because the pci_bus is only
> incidental and the caller doesn't care about it at all except for passing
> it to acpi_pci_get_bridge_handle().
> 
> It's relatively common to start with a pci_dev and look for an ACPI handle
> that corresponds to that device or the closest enclosing scope, so maybe
> there should be a way to do that directly.

Well, the bridge in question should be the parent of the device if I'm
not mistaken.  At least that's the assumption made by acpi_pci_find_companion().

> For pci_get_hp_params(), I think the current code is actually slightly
> buggy because we don't look for _HPP/_HPX on the device itself; we only
> look at the bridges upstream from it.
> 
> What I had in mind was something like the following (untested and not for
> application).

So perhaps pci_find_acpi_handle() below may be somewhat simpler?

> diff --git a/drivers/pci/hotplug/acpi_pcihp.c b/drivers/pci/hotplug/acpi_pcihp.c
> index 876ccc620440..5e95df56b8ae 100644
> --- a/drivers/pci/hotplug/acpi_pcihp.c
> +++ b/drivers/pci/hotplug/acpi_pcihp.c
> @@ -116,20 +116,11 @@ int acpi_get_hp_hw_control_from_firmware(struct pci_dev *pdev, u32 flags)
>  		string = (struct acpi_buffer){ ACPI_ALLOCATE_BUFFER, NULL };
>  	}
>  
> -	handle = ACPI_HANDLE(&pdev->dev);
> -	if (!handle) {
> -		/*
> -		 * This hotplug controller was not listed in the ACPI name
> -		 * space at all. Try to get acpi handle of parent pci bus.
> -		 */
> -		struct pci_bus *pbus;
> -		for (pbus = pdev->bus; pbus; pbus = pbus->parent) {
> -			handle = acpi_pci_get_bridge_handle(pbus);
> -			if (handle)
> -				break;
> -		}
> -	}
> -
> +	/*
> +	 * We did not find _OSC on the host bridge, so look for any
> +	 * enclosing device with an OSHP method.
> +	 */
> +	handle = pci_find_acpi_handle(pdev);
>  	while (handle) {
>  		acpi_get_name(handle, ACPI_FULL_PATHNAME, &string);
>  		dbg("Trying to get hotplug control for %s \n",
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index 6ebf8edc5f3c..3b3f0720fff0 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -246,14 +246,8 @@ int pci_get_hp_params(struct pci_dev *dev, struct hotplug_params *hpp)
>  {
>  	acpi_status status;
>  	acpi_handle handle, phandle;
> -	struct pci_bus *pbus;
>  
> -	handle = NULL;
> -	for (pbus = dev->bus; pbus; pbus = pbus->parent) {
> -		handle = acpi_pci_get_bridge_handle(pbus);
> -		if (handle)
> -			break;
> -	}
> +	handle = pci_find_acpi_handle(dev);
>  
>  	/*
>  	 * _HPP settings apply to all child buses, until another _HPP is
> @@ -279,6 +273,33 @@ int pci_get_hp_params(struct pci_dev *dev, struct hotplug_params *hpp)
>  }
>  EXPORT_SYMBOL_GPL(pci_get_hp_params);
>  
> +/*
> + * Search for an ACPI handle.  The PCI device itself may have one, or an
> + * upstream device (either a PCI-to-PCI bridge or a PCI host bridge) may
> + * have one.
> + */
> +acpi_handle pci_find_acpi_handle(struct pci_dev *pdev)
> +{
> +	struct device *dev;
> +	acpi_handle handle;
> +	struct pci_bus *bus;
> +
> +	dev = &pdev->dev;
> +	handle = ACPI_HANDLE(dev);
> +	while (!handle) {
> +		pdev = pci_physfn(pdev);
> +		bus = pdev->bus;
> +		if (pci_is_root_bus(bus))
> +			dev = bus->bridge;
> +		else {
> +			pdev = bus->self;
> +			dev = &pdev->dev;
> +		}
> +		handle = ACPI_HANDLE(dev);
> +	}
> +	return handle;
> +}
> +
>  /**
>   * pci_acpi_wake_bus - Root bus wakeup notification fork function.
>   * @work: Work item to handle.
> --
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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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