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

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Message-ID: <55C3FC93.6090008@roeck-us.net>
Date:	Thu, 06 Aug 2015 17:32:19 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Yinghai Lu <yinghai@...nel.org>
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 08/06/2015 04:32 PM, Yinghai Lu wrote:
> On Thu, Aug 6, 2015 at 9:18 AM, Guenter Roeck <linux@...ck-us.net> wrote:
>> On 08/06/2015 08:58 AM, Yinghai Lu wrote:
>
>> Ok, I admit that I am lost. Earlier it seemed that you were concerned about
>> this case, where no io window is available or a bus doesn't support io,
>> but a non-transparent child does. Now you seem to say that the
>> non-transparent
>> child would not be able to support IO either.
>>
>> For my education, can you list the possible options, and how you suggest
>> to solve them ? I can see the following situations.
>>
>> - root supports IO, but has no io window assigned
>> - root does not support IO and has or has not an IO window assigned
>> - a bridge does not support IO
>
> should have two cases:
> 1. root bus does not have io window exposed.
> 2. pci bridge io bar is not writable.
>
>>
>> For the transparent case, each of those should result in all children
>> not even trying to assign an IO window, which is what we want,
>> and what my patc set tries to do.
>>
>> How should those cases be handled for non-transparent bridges ?
>
> for case 2: current upstream code, no warning for the bridge itself,
> but have warning for devices under the bridge.
>

That warning is what I am trying to get rid of, because it is repeated
dozens of times with zero value.

> We only need to handle case 1, aka root bus does not have io port window.
>
> What about your setup, is it case 1 or case 2?
>

Assuming case 1) includes case 3), root bridge does not support IO,
I have both case 1 and 2.

Anyway, I think I am giving up. Sorry, I just fail to understand the
use case(s) you are trying to cover.

Why don't you submit a patch, I'll test it if it works for my use
case, and if it works we ask Bjorn to apply it. My problem is quite
simple: I don't want to get flooded with useless "no IO window" messages.
How it is solved doesn't matter to me, as long as it is solved.
Since you have a strong opinion on how it should be solved, we should
go with your solution and not keep turning in circles forever.

Thanks
Guenter

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