linux-kernel - Re: [PATCH] PCI: Set device power state to PCI

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Message-ID: <alpine.DEB.2.00.1110131525320.3519@kaball-desktop>
Date:	Thu, 13 Oct 2011 15:30:22 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Ajaykumar Hotchandani <ajaykumar.hotchandani@...cle.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: Set device power state to PCI_D0 for device without
 native PM support

On Mon, 10 Oct 2011, Ajaykumar Hotchandani wrote:
> On 10/06/2011 09:47 PM, Stefano Stabellini wrote:
> > On Thu, 6 Oct 2011, Yinghai Lu wrote:
> >> On Thu, Oct 6, 2011 at 3:39 AM, Stefano Stabellini
> >> <stefano.stabellini@...citrix.com>  wrote:
> >>> I had the same issue and sent a patch a while ago to fix it, adding
> >>>
> >>> current_state = PCI_D0 in acpiphp_glue.c:register_slot
> >>>
> >>> it is strange that this does not work for you:
> >>>
> >>> http://marc.info/?l=linux-kernel&m=129891002722845&w=2
> >> So guest os has to load acpiphp instead of pciehp?
> >
> > maybe pciehp needs to make sure that current_state = D0 in
> > pciehp_enable_slot, like acpiphp does
> Here, acpi hotplugging is involved.
> With your change in register_slot(), device will have proper power state when module is being loaded for the first time after booting.
> However, while unload of pci module; following is in pci_device_remove():
>          if (pci_dev->current_state == PCI_D0)
>                  pci_dev->current_state = PCI_UNKNOWN;
> 
> So, device power state state will remain PCI_UNKNOWN while module is loaded again. Subsequently, MSI write will do nothing.

Does this mean that this bug would actually trigger even with devices that
do support _EJ0 and power management?
Because acpi_pci_set_power_state won't set current_state to PCI_D0
because the "hotplug driver will take care of _PSx" (see
10b3dcae0f275e2546e55303d64ddbb58cec7599) but the hotplug driver is not
actually invoked when loading again a driver module of an existing pci
device (the example you mention above)?
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