linux-kernel - Re: [PATCH] pci: print out DMA mask info

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Date:	Fri, 10 Oct 2008 09:46:33 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Matthew Wilcox <matthew@....cx>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	grundler@...isc-linux.org, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci: print out DMA mask info

Matthew Wilcox wrote:
> 
> By the way, commit 8f286c33f1e838d631f4a3260b33efce4bc5973c is a really
> bad idea.  It is very helpful to see which bitmasks are used by real
> devices, and which ones aren't.  It should be reverted, IMO.
> 

why? did you point to wrong commit?

commit 8f286c33f1e838d631f4a3260b33efce4bc5973c
Author: Andrew Morton <akpm@...ux-foundation.org>
Date:   Thu Oct 18 03:05:07 2007 -0700

    stop using DMA_xxBIT_MASK
    
    Now that we have DMA_BIT_MASK(), these macros are pointless.
    
    Cc: Jeremy Fitzhardinge <jeremy@...p.org>
    Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 29b0285..101a2d4 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -13,9 +13,15 @@ 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))
 
-#define DMA_64BIT_MASK	(~0ULL)
+/*
+ * NOTE: do not use the below macros in new code and do not add new definitions
+ * here.
+ *
+ * Instead, just open-code DMA_BIT_MASK(n) within your driver
+ */
+#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)
--
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