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From: Yongji Xie <elohimes@gmail.com>
Date: Wed, 19 Apr 2017 10:12:07 +0800
Message-ID: <CAONzpcaGfO5bcSdjpX4NC=Ui9oTWORaj-v1vTDUTckPC5WWjqQ@mail.gmail.com>
Subject: Re: [PATCH v11 4/7] powerpc/powernv: Override pcibios_default_alignment()
 to force PCI devices to be page aligned
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
        Li Zhong <zhong@linux.vnet.ibm.com>,
        Alexey Kardashevskiy <aik@ozlabs.ru>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        Gavin Shan <gwshan@linux.vnet.ibm.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Paul Mackerras <paulus@samba.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
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On 19 April 2017 at 09:47, Michael Ellerman <mpe@ellerman.id.au> wrote:
> Bjorn Helgaas <bhelgaas@google.com> writes:
>
>> On Mon, Apr 17, 2017 at 4:36 PM, Bjorn Helgaas <bhelgaas@google.com> wrote:
>>> From: Yongji Xie <elohimes@gmail.com>
>>> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>>> index 6901a06da2f9..b724487cbd0f 100644
>>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
>>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>>> @@ -3287,6 +3287,11 @@ static void pnv_pci_setup_bridge(struct pci_bus *bus, unsigned long type)
>>>         }
>>>  }
>>>
>>> +static resource_size_t pnv_pci_default_alignment(struct pci_dev *pdev)
>>> +{
>>> +       return PAGE_SIZE;
>>> +}
>>
>> Is it necessary that pcibios_default_alignment() take a pci_dev
>> pointer?
>
> It's not necessary given the current implementation, obviously.
>
> But it did strike me as a good idea to pass it in case we ever want to
> do anything device specific in future.
>
>> I'd like this better if it were:
>>
>>   resource_size_t pcibios_default_alignment(void) { ... }
>>
>> because the last patch relies on the assumption that all resources of
>> *all* devices will be realigned to the same alignment.
>
> But I guess that precludes doing anything device specific, at least
> without further changes. So in that case it would be better if the API
> didn't include the pci_dev.
>
> Hopefully Yongji can confirm that there were no plans to use the
> pci_dev in future patches.
>

Yes, seems like pci_dev pointer doesn't match the assumption
that all resources will be realigned to the same alignment. It's OK
to me to remove it.

Thanks,
Yongji