linux-kernel - Re: [Resend PATCH 5/5] IA64/PCI/ACPI: Rework PCI root bridge ACPI resource conversion

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Message-ID: <CAErSpo5ye_Y=b7476cFuDi7-hW4bJzm+D99cTek+wNkWefs4DQ@mail.gmail.com>
Date:	Wed, 30 Oct 2013 10:23:26 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Lan Tianyu <tianyu.lan@...el.com>
Cc:	Tony Luck <tony.luck@...el.com>, Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Yinghai Lu <yinghai@...nel.org>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"Yoknis, Mike" <mike.yoknis@...com>,
	"Pearson, Greg" <greg.pearson@...com>
Subject: Re: [Resend PATCH 5/5] IA64/PCI/ACPI: Rework PCI root bridge ACPI
 resource conversion

On Wed, Oct 30, 2013 at 2:34 AM, Lan Tianyu <tianyu.lan@...el.com> wrote:
> On 2013年10月29日 01:32, Bjorn Helgaas wrote:
>>
>> On Sat, Oct 26, 2013 at 10:53 AM, Lan Tianyu <tianyu.lan@...el.com> wrote:
>>>
>>> On 10/24/2013 06:39 AM, Bjorn Helgaas wrote:
>>>>
>>>> On Fri, Oct 18, 2013 at 08:44:12PM +0800, Lan Tianyu wrote:
>>>>>
>>>>>
>>>>> On 10/18/2013 04:33 AM, Bjorn Helgaas wrote:
>>
>>
>>>>>> I wonder if it would make sense to make
>>>>>> acpi_dev_resource_address_space() ignore addr.translation_offset for
>>>>>> IO resources.  Or maybe ignore it if the _TTP (type translation) bit
>>>>>> is set?
>>>>>
>>>>>
>>>>>
>>>>> I wonder why current code doesn't check _TTP? The code in the
>>>>> add_io_space() seems to think _TTP is always set, right?
>>>>
>>>>
>>>> I think it's an oversight, and you should fix it.  I suggest that you
>>>> ignore the _TRA value when _TTP is set.  Obviously this only applies
>>>> to I/O port resources, since _TTP is only defined in the I/O Resource
>>>> Flag (Table 6-185 in ACPI 5.0 spec).
>>>
>>>
>>> _TTP is also defined in the Memory Resource flag, Please have a look at
>>> Table 6-184 in the ACPI 5.0 Spec.
>>
>>
>> Yes, you're right.  That would be for a host bridge that converts I/O
>> on the primary (upstream) side of the bridge to memory on the PCI
>> side.  I've never seen such a bridge, and I can't really imagine why
>> anybody would do that.  But I guess you should be able to safely
>> ignore _TRA when _TTP is set in either a MEM or IO descriptor, because
>> the same reasoning should apply to both.
>>
>>> I am not sure how to deal with _TTP unsetting io resource? _TTP unsetting
>>> mean the resource is IO on the primary side and also IO on the secondary
>>> side.
>>
>>
>> If _TTP is not set, I guess you would apply _TRA.  That's what you
>> already do for MEM descriptors, and think you should just do the same
>> for IO descriptors.  I would guess that having _TTP = 0 and _TRA != 0
>> is rare for IO descriptors, but I suppose it could happen.
>
>
> Yes, my concern is for the IO resource case of _TTP=0 and _TRA !=0. The
> only reason for this case I think of is that the IO resource offsets on
> the prime bus and second bus are different. In this case, we still need
> to pass _TRA to new_space() and the finial resource->start still should be
> acpi_resource->min + offset returned by add_io_space(), right?

No, I don't think so.  If the "phys_base" argument to new_space() is
non-zero, it is the base of an MMIO region that needs to be
ioremapped.  This is handling the _TTP=1 case, where the MMIO region
is translated by the bridge into an IO region on PCI.

If _TTP=0, the region is IO on both the upstream and downstream sides
of the host bridge, and we don't want to ioremap a new MMIO region for
it.  It might be part of the "legacy I/O port space," but that's
already covered elsewhere.

I don't think we need to add special handling for the _TTP=0 and _TRA
!= 0 case because I don't think it exists in the field.  If and when
it *does* exist, we'll know what to do.  In the meantime, it should
look just like the MEM path.

> If yes, I think _TRA can't be applied to IO resource in the
> acpi_dev_resource_address_space() regardless of the value of _TTP.
>
> BTW, Translation Sparse(_TRS) is only meaningful if _TTP is set.(Table
> 6-185). The add_io_space() doesn't check _TTP when set sparse. So this
> should be corrected?

Sure, I'm OK with this.  It's possible we could trip over a BIOS bug
where _TRS=1 but _TTP=0, but I think the risk is low because only
large ia64 boxes would use this, and there aren't very many of those.

Bjorn
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