linux-kernel - Re: [PATCH 4/5] infiniband: add "dmabarrier" argument to ib_umem

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Message-ID: <20071003175112.GP26752@sgi.com>
Date:	Wed, 3 Oct 2007 10:51:12 -0700
From:	akepner@....com
To:	David Miller <davem@...emloft.net>
Cc:	grundler@...isc-linux.org, jbarnes@...tuousgeek.org, jes@....com,
	randy.dunlap@...cle.com, rdreier@...co.com,
	James.Bottomley@...eleye.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] infiniband: add "dmabarrier" argument to ib_umem_get()

On Tue, Oct 02, 2007 at 08:10:23PM -0700, David Miller wrote:
> From: akepner@....com
> Date: Tue, 2 Oct 2007 19:49:06 -0700
> 
> > 
> > Pass a "dmabarrier" argument to ib_umem_get() and use the new 
> > argument to control setting the DMA_BARRIER_ATTR attribute on 
> > the memory that ib_umem_get() maps for DMA.
> > 
> > Signed-off-by: Arthur Kepner <akepner@....com>
> 
> Acked-by: David S. Miller <davem@...emloft.net>
> 
> However I'm a little unhappy with how IA64 achieves this.
> 
> The last argument for dma_map_foo() is an enum not an int,
> every platform other than IA64 properly defines the last
> argument as "enum dma_data_direction".  It can take one
> of several distinct values, it is not a mask.
> 
> This hijacking of the DMA direction argument is hokey at
> best, and at worst is type bypassing which is going to
> explode subtly for someone in the future and result in
> a long painful debugging session.
> ....

I don't dispute your point about abusing the enum here, it 
just seemed the least objectionable, and most expedient way 
to go.  But I'll add that ia64 isn't alone, x86_64 also uses 
an int for the final argument to its dma_map_* implementations.

-- 
Arthur

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