Subject: Re: [PATCH V4 2/6] powerpc/powernv: simplify the calculation of iov resource alignment

From: Alexey Kardashevskiy <[email-masked]>
Date: Fri, 2 Oct 2015 18:58:09 +1000

On 08/19/2015 12:01 PM, 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 extended with number of
> roundup_pow_of_two(total_vfs) or number of max PE number (256), the total
> size could be calculated by (vfs_expanded * VF_BAR_size).
>
> 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 8c031b5..e3e0acb 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -2988,12 +2988,16 @@ 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.

Out of curiosity - IOV BAR does NOT have to be aligned on other platforms?

> +	 *
> +	 * This function returns the total IOV BAR size if expanded or just the
> +	 * individual size if not.

Expanded vs. non-expanded means "using shared M64" (when it is split by 256 
segments) vs. "using entire M64"?

> +	 */
>   	align = pci_iov_resource_size(pdev, resno);
>   	if (pdn->vfs_expanded)
>   		return pdn->vfs_expanded * align;
>

-- 
Alexey