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

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Date:	Mon, 10 Oct 2011 17:32:09 +0530
From:	Ajaykumar Hotchandani <ajaykumar.hotchandani@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	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 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.

Thanks,
Ajay


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