On Mon, Oct 10, 2011 at 11:24:05AM +0200, Benjamin Herrenschmidt wrote:
> On Mon, 2011-10-10 at 11:16 +0200, Eli Cohen wrote:
>
> > Until then I think we need to have the logic working right on ppc and
> > measure if blue flame buys us any improvement in ppc. If that's not
> > the case (e.g because write combining is not working), then maybe we
> > should avoid using blueflame in ppc.
> > Could any of the guys from IBM check this and give us feedback?
>
> I don't have the necessary hardware myself to test that but maybe Thadeu
> can.
>
> Note that for WC to work, things must be mapped non-guarded. You can do
> that by using ioremap_prot() with pgprot_noncached_wc(PAGE_KERNEL) or
> ioremap_wc() (dunno how "generic" the later is).
I use the io mapping API:
at driver statrt:
priv->bf_mapping = io_mapping_create_wc(bf_start, bf_len);
if (!priv->bf_mapping)
err = -ENOMEM;
and then:
uar->bf_map = io_mapping_map_wc(priv->bf_mapping, uar->index <<
PAGE_SHIFT);
Will this work on ppc?
>
> >From there, you should get write combining provided that you don't have
> barriers between every access (ie those copy operations in their current
> form should do the trick).
>
> Cheers,
> Ben.
>
> > > Maybe it's time for us to revive those discussions about providing a
> > > good set of relaxed MMIO accessors with explicit barriers :-)
> > >
> > > Cheers,
> > > Ben.
> > >
>
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
