Date: Sat, 16 Aug 2003 17:39:52 +0300 (EEST)
From: Kai Makisara <Kai.Makisara@kolumbus.fi>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
cc: Manfred Spraul <manfred@colorfullife.com>,
       linux-kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] slab debug vs. L1 alignement
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On Sat, 16 Aug 2003, Benjamin Herrenschmidt wrote:

...
> THe low level driver can't do the bounce buffer thing, it has to be
> done at higher layers.
>
Agreed. A high-level driver must be able to handle this anyway because of
other constraints. The point is that this costs cpu cycles and bouncing
should be avoided if possible.

> > If an architecture has restrictions, they must, of course, be taken into
> > account. However, this should not punish architectures that don't have the
...
> > sizes. This would mean adding two more masks for each device (like the
> > current DMA address mask for a device).
>
> That won't help for buffers coming from higher layers that don't know
> the device they'll end up to
>
Agreed. This just enables the high-level driver to avoid bouncing. For
instance, in a P4 system it is usually not necessary to require 128 byte
alignment for DMA.

-- 
Kai
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