Re: [LKML] Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Wed, May 19, 2010 at 11:38:34PM +0900, FUJITA Tomonori wrote:
> On Wed, 19 May 2010 23:52:26 +1000
> Nick Piggin <npiggin@suse.de> wrote:
> 
> > On Wed, May 19, 2010 at 03:44:30PM +0200, Johannes Weiner wrote:
> > > On Wed, May 19, 2010 at 11:36:56PM +1000, Nick Piggin wrote:
> > > > On Wed, May 19, 2010 at 02:17:47PM +0100, David Woodhouse wrote:
> > > > >
> > > > > The 'cacheline aligned' misconception did manage to get into the ad7877
> > > > > driver in commit 3843384a though -- it now uses ____cacheline_aligned
> > > > > instead of __attribute__((__aligned__(ARCH_KMALLOC_MINALIGN))) as it
> > > > > should.
> > > > 
> > > > OK so long as there is not a "must be cacheline aligned" requirement.
> > > > Your proposal for a __dma_aligned attribute in an arch header looks
> > > > like a good idea there.
> > > 
> > > Would you happen to know of other potential users?  At this point I'd
> > > much rather just allocate the buffers dynamically and hide the issue
> > > nicely behind kmalloc().
> > 
> > I don't think we need to hide the fact that some platforms have
> > specific alignment restrictions for DMA. So if any drivers make use
> > of the alignment, I see no problem with __dma_aligned.
> 
> IIRC, such was proposed several times:
> 
> http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg12633.html
> 
> I guess that we agreed that it's better to tell driver writers to just
> use kmalloc.

It really dpeends on the size of the buffer. When I need a single byte I
really do not want to mess with separate kmalloced buffer.

If somebody coudl pick David's patch that would be great.

-- 
Dmitry