linux-kernel - Re: [PATCH] powerpc/iommu/ddw: Fix endianness

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Date:	Mon, 15 Sep 2014 19:18:08 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>,
	Alistair Popple <alistair@...ple.id.au>,
	Anton Blanchard <anton@...ba.org>,
	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Alexander Graf <agraf@...e.de>
Subject: Re: [PATCH] powerpc/iommu/ddw: Fix endianness

On Mon, 2014-09-15 at 18:41 +1000, Alexey Kardashevskiy wrote:
> On 09/09/2014 09:22 PM, Alexey Kardashevskiy wrote:
> > rtas_call() accepts and returns values in CPU endianness.

Sounds right.

> > of_read_number() accepts big-endian values but create.addr_hi/lo returned
> > by rtas_call() are in CPU endiannes.

Also sounds right.

> > The dynamic_dma_window_prop struct defines all members as BE so let's
> > make it true.

It does. But why does it do that? It seems to be allocated and setup in
enable_ddw() and then the only place I see it used is in
tce_setrange_multi_pSeriesLP()/tce_clearrange_multi_pSeriesLP(), which both
unpack it again. What am I missing?

> > struct dynamic_dma_window_prop {
> >         __be32  liobn;          /* tce table number */
> >         __be64  dma_base;       /* address hi,lo */
> >         __be32  tce_shift;      /* ilog2(tce_page_size) */
> >         __be32  window_shift;   /* ilog2(tce_window_size) */
> > };

We do read them from the device tree in find_existing_ddw_windows(), but if
that's the only place then the conversion to cpu endian should happen there.

> > diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> > index 7c1d77c..700020a 100644
> > --- a/arch/powerpc/platforms/pseries/iommu.c
> > +++ b/arch/powerpc/platforms/pseries/iommu.c
> > @@ -750,7 +750,7 @@ static void remove_ddw(struct device_node *np, bool remove_prop)
> >  		pr_debug("%s successfully cleared tces in window.\n",
> >  			 np->full_name);
> >  
> > -	ret = rtas_call(ddw_avail[2], 1, 1, NULL, liobn);
> > +	ret = rtas_call(be32_to_cpu(ddw_avail[2]), 1, 1, NULL, liobn);

The conversion should happen once where ever ddw_avail comes out of the device
tree, rather than everywhere it's used.

cheers



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