[ofa-general] Re: [PATCH 19/20] IB/ipath - add calls to new 7220 code and enable in build

[Ralph Campbell]

On Fri, 2008-04-04 at 14:15 -0700, Roland Dreier wrote:
>  > +enum ib_rate ipath_mult_to_ib_rate(unsigned mult)
>  > +{
>  > +	switch (mult) {
>  > +	case 8:  return IB_RATE_2_5_GBPS;
>  > +	case 4:  return IB_RATE_5_GBPS;
>  > +	case 2:  return IB_RATE_10_GBPS;
>  > +	case 1:  return IB_RATE_20_GBPS;
>  > +	default: return IB_RATE_PORT_CURRENT;
>  > +	}
>  > +}
> 
> Looks suspiciously like a copy of the existing mult_to_ib_rate() except
> it handles fewer cases... is there a reason to copy this?
> 
>  - R.

It looks similar but the values are reversed. This is converting
the ib_rate enum to a multiplier of the DDR clock rate which is
used as a counter to delay packets. So IB_RATE_2_5_GBPS is 8
times slower than IB_RATE_20_GBPS. The standard functions map
the enum to a multiplier of the slowest rate so
IB_RATE_2_5_GBPS is one. If I used the standard functions, I would
still need a lookup table to map 8->1, 1->8, etc.