cvs commit: src/share/man/man9 bus_dma.9

Scott Long scottl at
Wed Mar 1 15:50:40 PST 2006

John-Mark Gurney wrote:
> Ruslan Ermilov wrote this message on Thu, Mar 02, 2006 at 01:26 +0200:
>>On Tue, Feb 28, 2006 at 07:58:57PM +0000, John-Mark Gurney wrote:
>>>jmg         2006-02-28 19:58:57 UTC
>>>  FreeBSD src repository
>>>  Modified files:
>>>    share/man/man9       bus_dma.9 
>>>  Log:
>>>  update examples to use the correct terms that was never updated when the
>>>  earlier descriptions were gone over...
>>>  MFC after:      3 days
>>>  Revision  Changes    Path
>>>  1.32      +3 -3      src/share/man/man9/bus_dma.9
>>Not enough of fixing: "DMA read" and "DMA write" are also entangled here.
> Nope...  WRITE == DMA read...  Read the descriptions of the flags
> very carefully...  If you aren't confused, you don't understand it..
> The reason you're confused is the reason why everyone gets it wrong,
> and no one ever gets it correct the first time trying to figure out
> which one to use...

Think of it from the perspective of the driver doing an operation.  If 
the driver is reading a block off the disk, then you want to use the
PREREAD/POSTREAD operations.  Likewise for writes.  It is done this way
for clarity in the driver.  I can't imagine how many bugs we'd have if
write == read in the driver sources.


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