Re: [PARPORT] Re: Parport & DMA -- patch-2.2.7-tmw3

Philip Blundell (
Wed, 12 May 1999 22:33:05 +0100

Tim Waugh wrote:
>On Wed, 12 May 1999, Bert De Jonghe wrote:
>> Maybe parport_pc can have a private DMA-capable buffer (private_data
>> ?) allocated if DMA is configured ? The cost would be an extra copy
>> of the data into this buffer, but for me that's a price I'm willing to
>> pay to avoid making the high-level drivers more complex and putting PC
>> artifacts all over the place.
>I'd rather not take the extra copy for no reason.

Actually, this is quite a good suggestion. The low-level driver can inspect
the address of the buffer it's handed, see if it's suitable for DMA as it
stands (ie on an ISA machine, make sure it is entirely below the 16MB limit)
and either use it directly or copy it to a bounce buffer as necessary. So
yes, you will get an extra copy some of the time, but it might be worth it to
save on software complexity. The time to copy probably isn't that big a deal.


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This archive was generated by hypermail 2.0b3 on Wed 12 May 1999 - 17:33:35 EDT