netdev - Re: [PATCH] mlx4_en: fix transmit of packages when blue frame is enabled

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Date:	Mon, 10 Oct 2011 12:18:33 +0200
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Eli Cohen <eli@....mellanox.co.il>
Cc:	David Laight <David.Laight@...LAB.COM>, netdev@...r.kernel.org,
	Eli Cohen <eli@...lanox.co.il>, linuxppc-dev@...ts.ozlabs.org,
	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>,
	Yevgeny Petrilin <yevgenyp@...lanox.co.il>
Subject: Re: [PATCH] mlx4_en: fix transmit of packages when blue frame is
 enabled

On Mon, 2011-10-10 at 11:29 +0200, Eli Cohen wrote:
> 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?

That API has never been tested on ppc I suspect. We don't have
CONFIG_HAVE_ATOMIC_IOMAP (mostly because we never needed it, it
was designed and only ever used for Intel graphics before), so
it will fallback to:

static inline struct io_mapping *
io_mapping_create_wc(resource_size_t base, unsigned long size)
{
	return (struct io_mapping __force *) ioremap_wc(base, size);
}

Which should work (hopefully :-)

Cheers,
Ben.


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