linux-kernel - Re: [PATCH 1/1] unify DMA_..BIT

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Date:	Sat, 6 Oct 2007 10:37:35 +0200
From:	Borislav Petkov <bbpetkov@...oo.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org, muli@...ibm.com,
	satyam@...radead.org, amitkale@...xen.com,
	achim_leubner@...ptec.com
Subject: Re: [PATCH 1/1] unify DMA_..BIT_MASK definitions: v3.1

On Fri, Oct 05, 2007 at 02:00:50PM -0700, Andrew Morton wrote:
> On Fri, 05 Oct 2007 13:43:54 -0700
> Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> 
> > Andrew Morton wrote:
> > > From: Andrew Morton <akpm@...ux-foundation.org>
> > >
> > > Now that we have DMA_BIT_MASK(), these macros are pointless.
> > >   
> > 
> > Except, unfortunately, DMA_64BIT_MASK.  I guess we could special case
> > it, assuming this works in all the contexts the macro is used in (ie,
> > compile-time constant?):
> > 
> > #define DMA_BIT_MASK(n)	(((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
> > 
> 
> doh.  Thanks.
> 
> --- a/include/linux/dma-mapping.h~stop-using-dma_xxbit_mask-fix
> +++ a/include/linux/dma-mapping.h
> @@ -13,7 +13,7 @@ enum dma_data_direction {
>  	DMA_NONE = 3,
>  };
>  
> -#define DMA_BIT_MASK(n)	((1ULL<<(n))-1)
> +#define DMA_BIT_MASK(n)	(((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
>  
>  /*
>   * NOTE: do not use the below macros in new code and do not add new definitions
> @@ -21,7 +21,7 @@ enum dma_data_direction {
>   *
>   * Instead, just open-code DMA_BIT_MASK(n) within your driver
>   */
> -#define DMA_64BIT_MASK	(~0ULL)
> +#define DMA_64BIT_MASK	DMA_BIT_MASK(64)
>  #define DMA_48BIT_MASK	DMA_BIT_MASK(48)
>  #define DMA_47BIT_MASK	DMA_BIT_MASK(47)
>  #define DMA_40BIT_MASK	DMA_BIT_MASK(40)
>

Hi and sorry for the late reply. IMHO, this solution is the most concise and still
clear enough a macro to understand what it does after a quick scan (unlike
uglies like IO_COND() in lib/iomap.c¹, :)) And, as a next step, we probably
should do

perl -pi -e 's/DMA_(..)BIT_MASK/DMA_BIT_MASK($1)/g' *

after removing the #define DMA_..BIT_MASK defines in /include/linux/dma-mapping.h
and the other two headers in the original patch after the x86 merge.
Current git (9f34073b4e54ad58541e0e2b4a87f4f6c1460e21) contains about 394
instances of usage of those macros, including the #definitions.


¹ this is not a flame!
-- 
Regards/Gruß,
    Boris.
-
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