Subject: Re: [PATCH V2 2/6] powerpc/powernv: simplify the calculation of iov resource

From: Alexey Kardashevskiy <[email-masked]>
Date: Thu, 6 Aug 2015 20:15:55 +1000

On 08/06/2015 07:41 PM, Wei Yang wrote:
> On Thu, Aug 06, 2015 at 07:00:00PM +1000, Alexey Kardashevskiy wrote:
>> On 08/06/2015 02:51 PM, Gavin Shan wrote:
>>> On Wed, Aug 05, 2015 at 09:24:59AM +0800, Wei Yang wrote:
>>>> The alignment of IOV BAR on PowerNV platform is the total size of the IOV
>>>> BAR. No matter whether the IOV BAR is truncated or not, the total size
>>>> could be calculated by (vfs_expanded * VF size).
>>>>
>>>
>>> s/VF size/VF BAR size
>>>
>>> I think the changelog would be more explicit:
>>>
>>> The alignment of IOV BAR on PowerNV platform is the total size of the
>>> IOV BAR, no matter whether the IOV BAR is extended with number of max
>>> VFs or number of max PE number (256). The alignment can be calculated
>>> by (vfs_expaned * VF_BAR_size).
>>
>>
>>
>> Is that really a PowerNV-specific requirement or it is valid for
>> every platform (I suspect this is the case here)?
>>
>
> Currently, it is PowerNV-specific.

How is x86 different on this matter?
Why would we need this extra alignment, not just VF's BAR alignment?

>>
>> Also, what is the exact meaning of "expanded" in @vfs_expanded? It is
>> either 255 (if individual VF BARs are <= 64MB) or
>> roundup_pow_of_two(total_vfs) (which is something like 4 or 16). What
>> is expanded here?
>>
>
> PF's IOV BAR original size is (VF BAR size * total_vfs).
>
> After expanding, the IOV BAR size  is (VF BAR size * 256) or (VF BAR size *
> roundup_pow_of_two(total_vfs)).

Ufff, got it now. I'd store just an expanded IOV BAR size (not some magic 
VFs number) because this is what it actually is:
pdn->vfs_expanded * align

>>
>>>
>>>> This patch simplifies the pnv_pci_iov_resource_alignment() by removing the
>>>> first case.
>>>>
>>>> Signed-off-by: Wei Yang <[email-masked]>
>>>
>>> Reviewed-by: Gavin Shan <[email-masked]>
>>>
>>>> ---
>>>> arch/powerpc/platforms/powernv/pci-ioda.c |   14 +++++++++-----
>>>> 1 file changed, 9 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>>>> index 9b41dba..7192e62 100644
>>>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
>>>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>>>> @@ -2987,12 +2987,16 @@ static resource_size_t pnv_pci_iov_resource_alignment(struct pci_dev *pdev,
>>>> 						      int resno)
>>>> {
>>>> 	struct pci_dn *pdn = pci_get_pdn(pdev);
>>>> -	resource_size_t align, iov_align;
>>>> -
>>>> -	iov_align = resource_size(&pdev->resource[resno]);
>>>> -	if (iov_align)
>>>> -		return iov_align;
>>>> +	resource_size_t align;
>>>>
>>>> +	/*
>>>> +	 * On PowerNV platform, IOV BAR is mapped by M64 BAR to enable the
>>>> +	 * SR-IOV. While from hardware perspective, the range mapped by M64
>>>> +	 * BAR should be size aligned.
>>>> +	 *
>>>> +	 * This function return the total IOV BAR size if expanded or just the
>>>> +	 * individual size if not.
>>>> +	 */
>>>> 	align = pci_iov_resource_size(pdev, resno);
>>>> 	if (pdn->vfs_expanded)
>>>> 		return pdn->vfs_expanded * align;
>>>> --
>>>> 1.7.9.5
>>>>
>>>
>>
>>
>> --
>> Alexey
>

-- 
Alexey