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From: Alexander Serkov <serkov@ukrpost.net>
To: freebsd-hackers@freebsd.org
Date: Thu, 14 Aug 2003 01:45:45 +0300
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Subject: Why is ATAPI DMA disabled by default ?
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I use 5.1-current and have found that by default FreeBSD disables ATAPI's 
support for DMA transfers and thus uses CPU hungry PIO modes.
It even makes sysctl used to change this read-only.
I had changed the default value of atapi_dma to 1 in dev/ata/atapi-all.c to 1 
and it worked fine for me.
Can someone explain why it is disabled?