Subject: Re: [PATCH v6 18/42] powerpc/powernv: Allocate PE# in deasending order

From: Alexey Kardashevskiy <[email-masked]>
Date: Tue, 11 Aug 2015 00:39:02 +1000

On 08/06/2015 02:11 PM, Gavin Shan wrote:
> The available PE#, represented by a bitmap in the PHB, is allocated
> in ascending order.

Available PE# is available exactly because it is not allocated ;)

> It conflicts with the fact that M64 segments are
> assigned in same order. In order to avoid the conflict, the patch
> allocates PE# in descending order.

What kind of conflict?

>
> Signed-off-by: Gavin Shan <[email-masked]>
> ---
>   arch/powerpc/platforms/powernv/pci-ioda.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index 56b058c..1c950e8 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -161,13 +161,18 @@ static struct pnv_ioda_pe *pnv_ioda_reserve_pe(struct pnv_phb *phb, int pe_no)
>   static struct pnv_ioda_pe *pnv_ioda_alloc_pe(struct pnv_phb *phb)
>   {
>   	unsigned long pe;
> +	unsigned long limit = phb->ioda.total_pe_num - 1;
>
>   	do {
>   		pe = find_next_zero_bit(phb->ioda.pe_alloc,
> -					phb->ioda.total_pe_num, 0);
> -		if (pe >= phb->ioda.total_pe_num)
> +					phb->ioda.total_pe_num, limit);
> +		if (pe < phb->ioda.total_pe_num &&
> +		    !test_and_set_bit(pe, phb->ioda.pe_alloc))
> +			break;
> +
> +		if (--limit >= phb->ioda.total_pe_num)
>   			return NULL;
> -	} while(test_and_set_bit(pe, phb->ioda.pe_alloc));
> +	} while (1);

Usually, if it is "while(1)", then it is "while(1){}" rather than 
"do{}while(1)" :)

>
>   	return pnv_ioda_init_pe(phb, pe);
>   }
>

-- 
Alexey