linux-kernel - Re: [Patch v4 0/8] Consolidate ACPI PCI root common code into ACPI core

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Date:	Mon, 08 Jun 2015 11:59:46 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Mark Salter <msalter@...hat.com>
CC:	Al Stone <ahs3@...hat.com>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Marc Zyngier <marc.zyngier@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Yijing Wang <wangyijing@...wei.com>,
	Lv Zheng <lv.zheng@...el.com>,
	"lenb @ kernel . org" <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org, "x86 @ kernel . org" <x86@...nel.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [Patch v4 0/8] Consolidate ACPI PCI root common code into ACPI
 core

On 2015年06月05日 00:29, Jiang Liu wrote:
> On 2015/6/4 23:51, Mark Salter wrote:
>> On Thu, 2015-06-04 at 14:41 +0800, Jiang Liu wrote:
>>> On 2015/6/4 14:31, Hanjun Guo wrote:
>>>> Hi Jiang,
>>>>
>>>> On 2015年06月04日 09:54, Jiang Liu wrote:
>>>>> On 2015/6/4 4:27, Al Stone wrote:
>>>>>> On 06/02/2015 12:12 AM, Jiang Liu wrote:
>>>>>>> This patch set consolidates common code to support ACPI PCI root on x86
>>>>>>> and IA64 platforms into ACPI core, to reproduce duplicated code and
>>>>>>> simplify maintenance. And a patch set based on this to support ACPI
>>>>>>> based
>>>>>>> PCIe host bridge on ARM64 has been posted at:
>>>>>>
>>>>>> Link is missing (or it's a typo of some flavor).
>>>>> HI Al,
>>>>>      Sorry, I missed the link. It has been posted at:
>>>>> https://lkml.org/lkml/2015/5/26/207
>>>>
>>>> I failed to get io resources for PCI hostbridge  when I was testing PCI
>>>> on ARM64 QEMU, I debugged this for quite a while, and finally found out
>>>> that ACPI resource parsing for IO is not suitable for ARM64, because io
>>>> space for x86 is 64K, but 16M for ARM64.
>>>>
>>>> This issue is only found when the firmware representing the io resource
>>>> using the type ACPI_RESOURCE_TYPE_ADDRESS32, so the io address will
>>>> greater than 64k.
>>>>
>>>> In drivers/acpi/resource.c:
>>>>
>>>> static void acpi_dev_ioresource_flags(struct resource *res, u64 len,
>>>>                                        u8 io_decode, u8 translation_type)
>>>> {
>>>>          res->flags = IORESOURCE_IO;
>>>>
>>>> [...]
>>>>
>>>>          if (res->end >= 0x10003)
>>>>                  res->flags |= IORESOURCE_DISABLED | IORESOURCE_UNSET;
>>>>
>>>> [...]
>>>> }
>>>>
>>>> so the code will filter out res->end >= 0x10003, and in my case, it will
>>>> more than 64K, so we can't get the IO resources.
>>>>
>>>> I got a question, why we use if (res->end >= 0x10003) here?
>>>> I mean 64k will be 0x10000, and in that case, we should use
>>>> if (res->end >= 0x10000) here, not 0x10003, any history behind that?
>>>
>>> Hi Hanjun,
>>> This is a special tricky for x86. You may read a dword(four bytes) from
>>> IO port 0xffff, so the effective io port space is 0x10003 bytes.
>>>
>>
>> Is there something in ACPI spec which would limit PCI IO space to 64K?
>> PCI itself allows 32-bit IO addresses and at least some arm64 platforms
>> use PCI bus addresses above 64K for IO transactions. From a PCI view,
>> the (res->end >= 0x10003) check doesn't make sense. Am I missing
>> something?
> HI Mark,
> 	Something interesting here. According to my understanding,
> the actually limitations are
> 1) the maximum size for each IO port space is 64k,
> 2) each PCI segment may only have one IO port space assigned at most.
>
> Other than those, it's flexible for system designer to:
> 1) have multiple IO port spaces, each is 64K at most.
> 2) CPU may use MMIO transactions to access PCI IO space, and PCI host
>     bridge will do the translation from CPU side MMIO address to PCI side
>     IO port address.
>
> For example, we may have following configuration on IA64 platforms:
> 1) CPU side physical address [0x100000000-0x100010000] maps to IO space
>     [0x00000-0x10000] on PCI segment 0
> 2) CPU side physical address [0x100010000-0x100020000] maps to IO space
>     [0x00000-0x10000] on PCI segment 1
> And ACPI resource descriptor provides 'translation_offset' to support
> such an usage case. Hope this helps:)

Hi Jiang,

It seems the translation_offset for IA64 is assuming to zero in this
patch set, which have regressions if we use DworldIO() with offset
to report io port resources, am I missing something?

Thanks
Hanjun
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