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List:       freebsd-bugs
Subject:    kern/164651: Disabling DMA in new Freebsd 9.0 CAM drivers does not work
From:       "Russell J. Yount" <Russell.Yount () gmail ! com>
Date:       2012-01-31 0:48:16
Message-ID: 201201310048.q0V0mGKd097306 () red ! freebsd ! org
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> Number:         164651
> Category:       kern
> Synopsis:       Disabling DMA in new Freebsd 9.0 CAM drivers does not work
> Confidential:   no
> Severity:       non-critical
> Priority:       medium
> Responsible:    freebsd-bugs
> State:          open
> Quarter:        
> Keywords:       
> Date-Required:
> Class:          sw-bug
> Submitter-Id:   current-users
> Arrival-Date:   Tue Jan 31 00:50:10 UTC 2012
> Closed-Date:
> Last-Modified:
> Originator:     Russell J. Yount
> Release:        Freebsd 9.0
> Organization:
Individual
> Environment:
FreeBSD server8.localdomain 9.0-RELEASE FreeBSD 9.0-RELEASE #0: Sun Jan 15 03:16:02 \
EST 2012     root@system-u.localdomain:/ufs/disk1/kernel/9.0/usr/src/sys/i386/compile/NET4801 \
i386

FreeBSD server10.localdomain 9.0-RELEASE FreeBSD 9.0-RELEASE #0: Sat Jan 21 18:44:20 \
EST 2012     root@system-u.localdomain:/ufs/disk1/kernel/9.0/usr/src/sys/i386/compile/NET4801-NOCAM \
i386

> Description:
Soekris Engineering produced a number of early version of the net4801 that did not \
support DMA on Compact flash disks correctly. Compact flash cards that did support \
DMA would fail unless "hw.ata.ata_dma=0" was place in /boot/loader.conf to disable \
DMA transfers for the ad driver.

FreeBSD 9.0 when compiled with CAM support appears not to disable DMA and just hanges \
with disk light on. When CAM support is not compiled in FreeBSD 9.0 everything works \
as before.

The CAM subsystem appears not to support disabling DMA.

I have both net4801s that do and do not support DMA for Compact Flash Disks. The ones \
that support DMA do work correctly in FreeBSD 9.0. The problem described only affects \
early production models which did not support DMA.



  
> How-To-Repeat:
Using an old net4801 which does support DMA with a flash card that does.

I suspect DMA is not being disabled at all with CAM and could be tested with other \
disks.

Am willing to test fixes if needed.  
> Fix:


> Release-Note:
> Audit-Trail:
> Unformatted:
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