linux-kernel - Re: [PATCH v3] PCI: Only enable IO window if supported

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Date:	Wed, 5 Aug 2015 21:25:03 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v3] PCI: Only enable IO window if supported

On Wed, Aug 5, 2015 at 7:22 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> On 08/05/2015 06:38 PM, Yinghai Lu wrote:
>>
>> On Wed, Aug 5, 2015 at 6:14 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>>>
>>>
>>> It only can avoid warning with bridge, and still have warning on
>>> devices under the bridge.
>>>
>>> also would have problem on transparent bridges, like
>>>
>>> BRIDGE_A ---- BRIDGE_AA----DEVICE_AA
>>>                     |
>>>                     \-- BRIDGE_AB ---DEVICE_AB
>>>
>>> if only BRIDGE_A and BRIDGE_AA are transparent, and BRIDGE_AB is not.
>>>
>>> and if pci_bridge_supports_io() return false for BRIDGE_A.
>>>
>>> We will have all three bridges have PCI_BUS_FLAGS_SUPPORTS_IO cleared.
>>> so all will not been sized and will not get assigned io port resource.
>>>
>>> later DEVICE_AA could root bus io port as parent, and get io resource
>>> assigned.
>>> but DEVICE_AB will not get assigned.
>>>
>>> so we should get rid of pci_bridge_supports_io(), and just check root
>>> resource IO port.
>>
>>
>> I would suggest this version instead:
>>
>> Subject: [PATCH] PCI: Only try to assign io port only if root bus support
>> that
>>
>
> Bjorn had asked me to move the IO support check out of
> pci_bridge_check_ranges().
> It looks like you want to keep it there.
>
> Can you explain your reasons ? Sorry, I just don't understand.

in pci_alloc_child_bus(), child bus's bus_flags will be assigned with
parent's bus_flags.

so if one parent bus has bridge's io bar can not changed, then all
children bus will also
have same bus_flags, and their bridge io bar will not used.

then if BRIDGE_AB is not transparent, we do need to use it's bridge io bar.
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