Date: Fri, 15 Feb 2002 20:58:23 +0100 From: Cliff Sarginson <cliff@raggedclown.net> To: freebsd-questions@FreeBSD.ORG Subject: Re: DMA on ATAPI CD's [ Was Re: About printers ] Message-ID: <20020215195823.GA407@raggedclown.net> In-Reply-To: <20020215191055.50E1E5D09@ptavv.es.net> References: <20020215185850.GC1394@raggedclown.net> <20020215191055.50E1E5D09@ptavv.es.net>
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On Fri, Feb 15, 2002 at 11:10:55AM -0800, Kevin Oberman wrote: > > Date: Fri, 15 Feb 2002 19:58:50 +0100 > > From: Cliff Sarginson <cliff@raggedclown.net> > > Sender: owner-freebsd-questions@FreeBSD.ORG > > > > On Fri, Feb 15, 2002 at 10:25:16AM -0800, Kevin Oberman wrote: > > > > Date: Thu, 14 Feb 2002 22:46:58 +0100 > > > > From: Cliff Sarginson <cliff@raggedclown.net> > > > > Sender: owner-freebsd-questions@FreeBSD.ORG > > > > > > > > On Sat, Jan 09, 1999 at 05:09:35PM +0300, vanya wrote: > > > > > > > > <snip> (Best to keep unrelated questions in seperate posts). > > > > > > > > > And one question about DMA for EIDE disks and ATAPI CD. Is DMA automatically > > > > > enabled or user must turn on this option? > > > > > > > > I believe DMA is not enabled on ATAPI CD devices, I believe it is > > > > considered a source of possible instability in certain cases (I know > > > > of no proof for this..) .. you can forceably re-enable it by an entry > > > > in sysctl.conf. I have 2 IDE i/faces, with a hard drive and a CD/DVD > > > > on one slave and a CD R/W on another. My line looks as follows: > > > > > > > > hw.atamodes=dma,dma,dma,dma > > > > > > > > You will need to adjust this according to your actual IDE setup, > > > > (i.e. how your ide's are actually configured)... > > > > > > > > "man 8 sysctl.conf" may help. > > > > > > On almost all systems you really want to add hw.ata.atapi_dma="1" to > > > /boot/loader.conf to enable DMA on ATAPI devices. > > > > > > The reason it is disabled by default is that some early ATAPI > > > controllers did not work correctly (at all) in DMA mode. Since it is > > > considered critical that CDs be accessible from the GENERIC kernel to > > > do the initial installation, all ATAPI access had to default to PIO. > > > > > > The only way to be sure about this is to turn on DMA and see of the CD > > > works. (It almost certainly will.) > > > > > > This is a parameter that must be set before the ATA driver is started, > > > so it cannot be put in sysctl.conf. It must be in /boot/loader.conf. > > > > > I think this is incorrect, it can be put in sysctl.conf, and I believe > > it works if you do it as I stated. > > When I try this I get: > sysctl: oid 'hw.ata.atapi_dma' is read only > Mmm. Now I am confused (what's new ?). What I do, is as stated in my post, is to adjust the parameter hw.atamodes to enable dma on the ide devices. What you are saying, or demonstrating, is the adjustment of the hw.ata.atapi_dma, variable cannot be done except at boot time. Now I am a bit confused about the relationship between these two variables. I am under the impression that what I do enables DMA on the said devices (I see no reason why it cannot be dynamically changed)..but doing what you suggest does indeed show up in dmesg as the CD devices using DMA instead of PIO ) I just tried it. So maybe I am under a false impression here, but a sysctl -a does show what I do as being accepted. So the question remains, am I under a false impression that what I do has any effect whatsoever ? It certainly does not generate a syslog message when I change them..is there any other way to tell ? Mmm. -- Regards Cliff To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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