Re: [PATCH] pci: print out DMA mask info

[Yinghai Lu <yinghai@kernel.org>]

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@linux-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@goop.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-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)