linux-kernel - Re: [PATCH 10/11] XEN / PCI: Remove the dependence on arch x86 when PCI

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Date:	Wed, 27 May 2015 11:55:45 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Arnd Bergmann <arnd@...db.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yijing Wang <wangyijing@...wei.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Mark Salter <msalter@...hat.com>, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>
Subject: Re: [PATCH 10/11] XEN / PCI: Remove the dependence on arch x86 when
 PCI_MMCONFIG=y

On 2015年05月26日 23:44, Boris Ostrovsky wrote:
> On 05/26/2015 10:54 AM, Tomasz Nowicki wrote:
>> On 26.05.2015 16:00, Boris Ostrovsky wrote:
>>> On 05/26/2015 09:54 AM, Boris Ostrovsky wrote:
>>>> On 05/26/2015 08:49 AM, Hanjun Guo wrote:
>>>>> In drivers/xen/pci.c, there are arch x86 dependent codes when
>>>>> CONFIG_PCI_MMCONFIG is enabled, since CONFIG_PCI_MMCONFIG
>>>>> depends on ACPI, so this will prevent XEN PCI running on other
>>>>> architectures using ACPI with PCI_MMCONFIG enabled (such as ARM64).
>>>>>
>>>>> Fortunatly, it can be sloved in a simple way. In drivers/xen/pci.c,
>>>>> the only x86 dependent code is if ((pci_probe & PCI_PROBE_MMCONF) ==
>>>>> 0),
>>>>> and it's defined in asm/pci_x86.h, the code means that
>>>>> if the PCI resource is not probed in PCI_PROBE_MMCONF way, just
>>>>> ingnore the xen mcfg init. Actually this is duplicate, because
>>>>> if PCI resource is not probed in PCI_PROBE_MMCONF way, the
>>>>> pci_mmconfig_list will be empty, and the if (list_empty())
>>>>> after it will do the same job.
>>>>>
>>>>> So just remove the arch related code and the head file, this
>>>>> will be no functional change for x86, and also makes xen/pci.c
>>>>> usable for other architectures.
>>>>>
>>>>> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
>>>>> CC: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>>>>> CC: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>>>>> ---
>>>>>   drivers/xen/pci.c | 6 ------
>>>>>   1 file changed, 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/xen/pci.c b/drivers/xen/pci.c
>>>>> index 6785ebb..9a8dbe3 100644
>>>>> --- a/drivers/xen/pci.c
>>>>> +++ b/drivers/xen/pci.c
>>>>> @@ -28,9 +28,6 @@
>>>>>   #include <asm/xen/hypervisor.h>
>>>>>   #include <asm/xen/hypercall.h>
>>>>>   #include "../pci/pci.h"
>>>>> -#ifdef CONFIG_PCI_MMCONFIG
>>>>> -#include <asm/pci_x86.h>
>>>>> -#endif
>>>>>
>>>>>   static bool __read_mostly pci_seg_supported = true;
>>>>>
>>>>> @@ -222,9 +219,6 @@ static int __init xen_mcfg_late(void)
>>>>>       if (!xen_initial_domain())
>>>>>           return 0;
>>>>>
>>>>> -    if ((pci_probe & PCI_PROBE_MMCONF) == 0)
>>>>> -        return 0;
>>>>> -
>>>>>       if (list_empty(&pci_mmcfg_list))
>>>>>           return 0;
>>>>>
>>>>
>>>> (+Stefano who is Xen ARM maintainer)
>>>>
>>>> This will not build on x86 since pci_mmcfg_list since, for example,
>>>> pci_mmcfg_list is declared in pci_x86.h.
>>>
>>>
>>> And now really with Stefano and with parsable first sentence, sorry:
>>>
>>>
>>> This will not build on x86 since pci_mmcfg_list, for example, is
>>> declared in pci_x86.h.
>>
>> With this patch set, not any more. Please see preceding patches.
>
>
> OK, I didn't notice this was part of a series.

Sorry, I didn't cc you all of those patches.

>
> Then if not having PCI_PROBE_MMCONF bit set is indeed equivalent to
> list_empty(&pci_mmcfg_list), is there any reason for this flag to
> (continue to) exist? (and also for pci_mmcfg_arch_init_failed.)

I think PCI_PROBE_MMCONF bit is needed for early init of pci mmconfig in
the x86 arch related code, but for xen_mcfg_late(), it's called after
acpi_init() which the mmconfig is ready for use if it's available (the
pci_mmcfg_list is empty or not), so not having PCI_PROBE_MMCONF bit set
is equivalent list_empty(&pci_mmcfg_list) is not suitable for all cases,
but I think it will be ok after mmconfig is initialized.

I think my change log is misleading and needs updating :)

Thanks
Hanjun
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