linux-kernel - Re: [PATCH] PCI: Remove duplicate pci_disable

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Date:	Fri, 26 Apr 2013 17:41:04 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Huang Ying <ying.huang@...el.com>,
	David Bulkow <David.Bulkow@...atus.com>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jiang Liu <jiang.liu@...wei.com>
Subject: Re: [PATCH] PCI: Remove duplicate pci_disable_device for pcie port

On 2013/4/26 14:20, Yinghai Lu wrote:
> On Thu, Apr 25, 2013 at 9:02 PM, Yijing Wang <wangyijing@...wei.com> wrote:
>> Hi Yinghai,
>>    We should not remove this additional pci_disable_device().
>> Because we enable pcie port device twice before. The first is pci_enable_brides(),
>> in x86, it was called in pci_assign_unassigned_resources(). The second in pcie_port_device_register().
>> So we should call pci_disable_device() twice for pci_dev->enable_cnt balance.
>>
>> But there is still a problem here. If we unbind a pcie port device pcie port driver, we can not
>> use its child devices again, because this pcie port device was disabled absolutely.
>>
>> So I think we should move the second pci_disable_device() to remove.c.
>>
>> I sent this patch to Bjorn and following is Bjorn reply
>> "And it's not clear to me whether unbinding the
>> pcie port driver should disable the bridge at all.  I think one could
>> argue that the bridge should remain functional even if the driver is
>> unloaded, because the PCI core *enables* the bridge even if the driver
>> is never loaded."
>>
>> Yinghai, how do you think about this issue?
> 

Hi Yinghai,
   Thanks for your comment!
We enable_bridges in PCI core code, so I think we should disable device in remove.c(PCI core level),
another reason is call second pci_disable_device() in pci_stop_bus_device() is safe, because all child device
has been stopped(unbind driver already).

> 1. we always enable bridges after assign unassigned resource for boot path
> and hotplug path.
> we should never call disable for that.

I agree "we should never call second disable" unless we stop this sub pci-tree().

Maybe the attached patch last letter is not safe enough, should wait pci bridge complete
to stop itself, then call the second pci_disable_device().

> 
> 2. driver should be keep enable/disable during probe/remove

I agree, use enable/disable balance is better.

> 
> looks like we need to rethink pci enable bridge.
> 
> if we want to enable one pci device, we should go up  to enable all bridges till
> root.

Yes, now we enable pci bridges from root to end. like in pci_assign_unassigned_resources().

> 
> let if we disable one pci device, we need to go up to disable bridge if its all
> pci device children get disabled.

Yes, This is what I think too. It seems like we only can do this in remove.c

> 
> if there is pci driver is bound with bridge device, those
> disable/enable bridge should be skipped.

Hmm, currently system achieve this by checking pci_dev->enable_cnt.

> 
> Thanks
> 
> Yinghai
> 
> .
> 


-- 
Thanks!
Yijing

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