lkml.org 
[lkml]   [2015]   [Apr]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Bugfix v3] x86/PCI/ACPI: Fix regression caused by commit 63f1789ec716
On 2015/4/10 8:28, Rafael J. Wysocki wrote:
> On Fri, Apr 10, 2015 at 12:37 AM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>> On Thursday, April 09, 2015 05:00:08 PM Bjorn Helgaas wrote:
>>> On Thu, Apr 9, 2015 at 4:37 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>>>> On Thursday, April 09, 2015 10:50:02 AM Jiang Liu wrote:
>>>>> On 2015/4/9 7:44, Rafael J. Wysocki wrote:
>>>>>> On Wednesday, April 08, 2015 01:48:46 PM Jiang Liu wrote:
>>>>>>> On 2015/4/7 8:28, Rafael J. Wysocki wrote:
>>>>>>>> On Friday, April 03, 2015 10:04:11 PM Bjorn Helgaas wrote:
>>>>>>>>> Hi Jiang,
>>>>>>> <snip>
>>>>>>>>>> Currently acpi_dev_filter_resource_type() is only used by ACPI pci
>>>>>>>>>> host bridge and IOAPIC driver, so it shouldn't affect other drivers.
>>>>>>>>>
>>>>>>>>> We should assume it will eventually be used for all ACPI devices,
>>>>>>>>> shouldn't we?
>>>>>>>>
>>>>>>>> I'm not sure about that, really. In fact, I'd restrict its use to devices
>>>>>>>> types that actually can "produce" resources (ie. do not require the resources
>>>>>>>> to be provided by their ancestors or to be available from a global pool).
>>>>>>>>
>>>>>>>> Otherwise we're pretty much guaranteed to get into trouble.
>>>>>>>>
>>>>>>>> And all of the above rules need to be documented in the kernel source tree
>>>>>>>> or people will get confused.
>>>>>>> Hi Rafael,
>>>>>>> How about following comments for acpi_dev_filter_resource_type()?
>>>>>>> Thanks!
>>>>>>> Gerry
>>>>>>> --------------------------------------------------------------------
>>>>>>> /**
>>>>>>> * According to ACPI specifications, Consumer/Producer flag in ACPI resource
>>>>>>> * descriptor means:
>>>>>>> * 1(CONSUMER): This device consumes this resource
>>>>>>> * 0(PRODUCER): This device produces and consumes this resource
>>>>>>> * But for ACPI PCI host bridge, it is interpreted in another way:
>>>>>>
>>>>>> So first of all, this leads to a question: Why is it interpreted for ACPI PCI
>>>>>> host bridges differently?
>>>>>>
>>>>>> Is it something we've figured out from experience, or is there a standard
>>>>>> mandating that?
>>>>> Hi Rafael,
>>>>> I think we got this knowledge by experiences. PCI FW spec only
>>>>> states _CRS reports resources assigned to the host bridge by firmware.
>>>>> There's no statement about whether the resource is consumed by host
>>>>> bridge itself or provided to it's child bus/devices. On x86/IA64 side,
>>>>> the main resource consumed by PCI host bridge is IOPORT 0xCF8-0xCFF,
>>>>> but not sure about ARM64 side. So how about:
>>>>
>>>> This:
>>>>
>>>>> PCI Firmware specification states that _CRS reports resources
>>>>> assigned to the host bridge, but there's no way to tell whether
>>>>> the resource is consumed by host bridge itself or provided to
>>>>> its child bus/devices.
>>>>
>>>> looks OK to me, but I'd replace the below with something like:
>>>>
>>>> "However, experience shows, that in the PCI host bridge case firmware writers
>>>> expect the resource to be provided to devices on the bus (below the bridge) for
>>>> consumption entirely if its Consumer/Producer flag is clear. That expectation
>>>> is reflected by the code in this routine as follows:".
>>>
>>> What a mess. The spec is regrettably lacking in Consumer/Producer
>>> specifics. But I don't see what's confusing about the descriptors
>>> that have Consumer/Producer bits.
>>>
>>> QWord, DWord, and Word descriptors don't seem to have a
>>> Consumer/Producer bit, but they do contain _TRA, so they must be
>>> intended for bridge windows. Can they also be used for device
>>> registers? I don't know.
>>>
>>> The Extended Address descriptor has a Consumer/Producer bit, and I
>>> would interpret the spec to mean that if the flag is clear (the device
>>> produces and consumes this resource), the resource is available on the
>>> bus below the bridge, i.e., the bridge consumes the resource on its
>>> upstream side and produces it on its downstream side.
>>
>> OK, that makes sense for bridges.

>>> If the bit were
>>> set (the device only consumes the resource), I would expect that to
>>> mean the descriptor is for bridge registers like 0xcf8/0xcfc that
>>> never appear on the downstream side.
>>
>> That part is clear. What is not clear is whether or not we can *always*
>> expect the resources with Consumer/Producer *clear* to be produced on the
>> downstram side. That appears to be the case for host bridges if my
>> understanding of things is correct, but is it the case in general?
>>
>>> Maybe I'm reading the spec too naively, but this doesn't seem a matter
>>> of experience.
>>
>> Well, the specification is not clear enough in that respect, at least as
>> far as I can say, or maybe it is, but then does firmware always follow that
>> interpretation?
>
> So I guess I'd like to propose to go back to the 3.19 behavior for PCI host
> bridges and then to handle the IOAPIC as a separate case.
>
> We can think about consolidating the two later.
>
> Any objections to doing that?
Hi Rafael,
When reverting to the behavior before v3.19, I found a simpler
solution. The logic before v3.19 is:
on x86 and IA64, all IO port and MMIO resources assigned to PCI host
bridge are available to child bus/devices, except one special case to
filter out IO port[0xCF8-0xCFF] for PCI configuration space access.

And with pre-v3.19 kernels, all IO port defined by IO and fixed_IO
resource descriptors are ignored to filter out IO port[0xCF8-0xCFF].

So I plan to make following change to revert to the behavior before
v3.19:
1) make acpi_dev_filter_resource_type() filter descriptors based on
descriptor type, and don't check consumer_producer flag anymore.
2) use IORESOURCE_IO_FIXED flag to filter out io and fixed_io resource
descriptors.
3) x86 ACPI pci host bridge driver calls acpi_dev_filter_resource_type()
with flag IORESOURCE_IO_FIXED,

By this way, we could keep acpi_dev_filter_resource_type()
as a generic interface and could be reused. And the change
is small too. Any comments?

Thanks!
Gerry
> Rafael
>


\
 
 \ /
  Last update: 2015-04-13 07:01    [W:0.105 / U:0.408 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site