Message-ID: <5570447D.3020705@linaro.org>
Date:	Thu, 04 Jun 2015 20:28:45 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Arnd Bergmann <arnd@...db.de>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yijing Wang <wangyijing@...wei.com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	"msalter@...hat.com" <msalter@...hat.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [PATCH 05/11] x86, pci, acpi: Move arch-agnostic MMCONFIG (aka
 ECAM) and ACPI code out of arch/x86/ directory

On 2015年06月04日 18:22, Lorenzo Pieralisi wrote:
> Hi Hanjun,
>
> On Thu, Jun 04, 2015 at 10:28:17AM +0100, Hanjun Guo wrote:
>> Hi Lorenzo,
>>
>> On 2015???06???02??? 21:32, Lorenzo Pieralisi wrote:
>>> On Wed, May 27, 2015 at 09:06:26AM +0100, Tomasz Nowicki wrote:
>>>> On 26.05.2015 19:08, Will Deacon wrote:
>>>>> On Tue, May 26, 2015 at 01:49:18PM +0100, Hanjun Guo wrote:
>>>>>> From: Tomasz Nowicki <tomasz.nowicki@...aro.org>
>>>>>>
>>>>>> ECAM standard and MCFG table are architecture independent and it makes
>>>>>> sense to share common code across all architectures. Both are going to
>>>>>> corresponding files - ecam.c and mcfg.c
>>>>>>
>>>>>> While we are here, rename pci_parse_mcfg to acpi_parse_mcfg.
>>>>>> We already have acpi_parse_mcfg prototype which is used nowhere.
>>>>>> At the same time, we need pci_parse_mcfg been global so acpi_parse_mcfg
>>>>>> can be used perfectly here.
>>>>>>
>>>>>> Signed-off-by: Tomasz Nowicki <tomasz.nowicki@...aro.org>
>>>>>> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
>>>>>> Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
>>>>>> ---
>>>>>>     arch/x86/Kconfig               |   3 +
>>>>>>     arch/x86/include/asm/pci_x86.h |  33 ------
>>>>>>     arch/x86/pci/acpi.c            |   1 +
>>>>>>     arch/x86/pci/mmconfig-shared.c | 244 +---------------------------------------
>>>>>>     arch/x86/pci/mmconfig_32.c     |   1 +
>>>>>>     arch/x86/pci/mmconfig_64.c     |   1 +
>>>>>>     arch/x86/pci/numachip.c        |   1 +
>>>>>>     drivers/acpi/Makefile          |   1 +
>>>>>>     drivers/acpi/mcfg.c            |  57 ++++++++++
>>>>>>     drivers/pci/Kconfig            |   7 ++
>>>>>>     drivers/pci/Makefile           |   5 +
>>>>>>     drivers/pci/ecam.c             | 245 +++++++++++++++++++++++++++++++++++++++++
>>>>>
>>>>> Why can't we make use of the ECAM implementation used by pci-host-generic
>>>>> and drivers/pci/access.c?
>>>>
>>>> We had that question when I had posted MMCFG patch set separately,
>>>> please see:
>>>> https://lkml.org/lkml/2015/3/11/492
>>>
>>> Yes, but the real question is, why do we need to have PCI config space
>>> up and running before a bus struct is even created ? I think the reason is
>>> the PCI configuration address space format (ACPI 6.0, Table 5-27, page
>>> 108):
>>>
>>> "PCI Configuration space addresses must be confined to devices on
>>> PCI Segment Group 0, bus 0. This restriction exists to accommodate
>>> access to fixed hardware prior to PCI bus enumeration".
>>>
>>> On HW reduced platforms I do not even think this is required at all,
>>> we have to look into this to avoid code duplication that might well
>>> turn out useless.
>>
>> This is only for the fixed hardware, which will be not available for
>> ARM64 (reduced hardware mode), but in Generic Hardware Programming
>> Model, we using OEM-provided ACPI Machine Language (AML) code to access
>> generic hardware registers, this will be available for reduced hardware
>> too.
>>
>> So in ACPI spec, it says: (ACPI 6.0 page 66, last paragraph)
>>
>> ACPI defines eight address spaces that may be accessed by generic
>> hardware implementations. These include:
>> * System I/O space
>> * System memory space
>> * PCI configuration space
>> * Embedded controller space
>> * System Management Bus (SMBus) space
>> * CMOS
>> * PCI BAR Target
>> * IPMI space
>>
>> So if any device using the PCI address space for control, such
>> as a system reset control device, its address space can be reside
>> in PCI configuration space (who can prevent a OEM do that crazy
>> thing? :) ), and it should be accessible before the PCI bus is
>> created.
>
> Us, by changing attitude and questioning features whose usefulness
> is questionable. I will look into this and raise the point, I am not
> thrilled by the idea of adding another set of PCI accessor functions
> and drivers because we have to access a register through PCI before
> enumerating the bus (and on arm64 this is totally useless since
> we are not meant to support fixed HW anyway). Maybe we can make acpica
> code use a "special" stub (ACPI specific, PCI configuration space address
> space has restrictions anyway), I have to review this set in its
> entirety to see how to do that (and I would kindly ask you to do
> it too, before saying it is not possible to implement it).

I'm willing to do that, actually, if we don't need a mechanism to
access PCI config space before the bus is created, the code can be
simplified a lot.

Thanks for your help and patient.

Hanjun
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