Message-ID: <20131031130002.GA9862@google.com>
Date:	Thu, 31 Oct 2013 07:00:02 -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 Thu, Oct 31, 2013 at 10:26:03AM +0800, Lan Tianyu wrote:
> On 2013年10月31日 00:23, Bjorn Helgaas wrote:
> > 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.
> 
> 
> OK. I get it. acpi_dev_resource_address_space() will only apply _TRA to
> resource ->start and ->end for both mem and io resource when _TTP=0. In
> the add_window(), the offset returned by add_io_space() will be added
> directly to ->start and ->end.
> 
> add_window() {
> 	...
> 	if (resource->flags & IORESOURCE_MEM) {
> 		root = &iomem_resource;
> 		offset = addr.translation_offset;

I can wait for your patch to see the whole thing, but I would expect
"offset = 0" here.  For MEM resources, the arch code should not need to
look inside "addr" at all.

> 	} else if (resource->flags & IORESOURCE_IO) {
> 		root = &ioport_resource;
> 
> 		offset = add_io_space(info, &addr);
> 		if (offset == ~0)
> 			return AE_OK;
> 
> 		resource->start += offset;
> 		resource->end += offset;
> 	} else
> 		return AE_OK;
> 
> 	...
> }
> 
> > 
> >> 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.
> > 
> 
> Ok. I will add a check for _TTP before setting sparse. Something likes this.
> 
> add_io_space()
> {
> ...
> if (addr->info.io.translation == ACPI_TYPE_TRANSLATION &&
>     addr->info.io.translation_type == ACPI_SPARSE_TRANSLATION)
> 	sparse = 1;
> ...
> }
> 
> 
> 
> > Bjorn
> > 
> 
> 
> -- 
> Best regards
> Tianyu Lan
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