Date: Fri, 30 Jul 2004 15:02:48 -0400 From: Chuck Swiger <cswiger@mac.com> To: =?ISO-8859-1?Q?S=F8ren_Schmidt?= <sos@DeepCore.dk> Cc: release@freebsd.org Subject: Re: Is there still sufficient reason for hw.ata.atapi_dma being 0 by default? Message-ID: <410A9B58.8000502@mac.com> In-Reply-To: <410A47C7.1080808@DeepCore.dk> References: <410A3833.7030502@portaone.com> <410A47C7.1080808@DeepCore.dk>
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Søren Schmidt wrote:
> Maxim Sobolev wrote:
>> Since high-speed CD-RW/DVD-RW recorders (32x - 52x) are commodity now
>> IMO it makes sense to review hw.ata.atapi_dma default of 0, since
>> apparently PIO mode can't support necessary sustained data transfer
>> rates anymore. For example I had had problems burning RWs on 16-24x
>> with several drives in PIO mode, which gone when I've switched to DMA.
Before CD burners became common, having this sysctl default to zero was almost
entirely harmless: people would simply read from CD-ROM drives slower than
optimal. If we change the default to one, people with fast burners will no
longer generate coasters by default too. In other words, Maxim has provided a
pretty good reason for changing the default of atapi_dma, I think. :-)
> Hmm, things are still messy, but most drives that support UDMA33 can do
> ATAPI dma. However, that is only part of the equation, the chipset has
> its hands in there as well, and unfortunatly there seems to be no good
> way to detect when it works and when it doesnt.
If the chipset is broken, why doesn't it default to using PIO4 rather than
UDMA? :-) Anyway, doesn't there exist fallback code in dev/ata/ata-disk.c:
/* if this is a UDMA CRC error, reinject request */
[ ... ]
printf(" falling back to PIO mode\n");
...which will switch a device generating errors from UDMA mode to PIO? Can
this check also turn off using atapi_dma (if using PIO doesn't already imply
not using DMA)?
--
-Chuck
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