[Soekris] net5501 ATA UDMA mode problem with FreeBSD 7.0

[Martin Johnson]

On 24 May 2008, at 16:27, Martin Johnson wrote:

> I'm upgrading a net5501 with a Travelstar E7K100 IDE drive from  
> FreeBSD 6.2 to 7.0.   FreeBSD 6.2 set the IDE controller up in  
> UDMA33 mode, but unfortunately 7.0 chooses UDMA100.   From my tests,  
> the fastest safe setting for this hardware appears to be UMDA66, as  
> UDMA100 gives  occasional errors such as "ad0: WARNING - READ_DMA  
> UDMA ICRC error (retrying request) LBA=3871".  This is the same on  
> comBIOS versions 1.32i and 1.33.
>
> Is there any way to force FreeBSD 7.0 to use UDMA66, or failing  
> that, UDMA33 ?
> ...
> It would be nice if /boot/loader.conf had a switch for this...

OK, now it does...   Here is a DIFF against /usr/src/sys/dev/ata/ata- 
all.c in FreeBSD 7.0-RELEASE.    It adds a sysctl called  
"hw.ata.ata_dma_limit", which places an upper limit to the ATA UDMA  
mode that can be used.  With this patch, if you set
	hw.ata.ata_dma_limit="4"
in /boot/loader.conf, then the fastest possible mode will be UDMA66.   
The hw.ata.ata_dma_limit setting will never increase the UDMA speed,  
only decrease it.

Hope this is useful,

- Martin.

80a81
 > static int ata_dma_limit = 6;
87a89,91
 > TUNABLE_INT("hw.ata.ata_dma_limit", &ata_dma_limit);
 > SYSCTL_INT(_hw_ata, OID_AUTO, ata_dma_limit, CTLFLAG_RDTUN,  
&ata_dma_limit, 0,
 > 	   "ATA disk DMA mode limit");
903c907
< 	if (ap->udmamodes & 0x40)
---
 > 	if (ap->udmamodes & 0x40  &&  ata_dma_limit >= 6)
905c909
< 	if (ap->udmamodes & 0x20)
---
 > 	if (ap->udmamodes & 0x20  &&  ata_dma_limit >= 5)
907c911
< 	if (ap->udmamodes & 0x10)
---
 > 	if (ap->udmamodes & 0x10  &&  ata_dma_limit >= 4)
909c913
< 	if (ap->udmamodes & 0x08)
---
 > 	if (ap->udmamodes & 0x08  &&  ata_dma_limit >= 3)
911c915
< 	if (ap->udmamodes & 0x04)
---
 > 	if (ap->udmamodes & 0x04  &&  ata_dma_limit >= 2)
913c917
< 	if (ap->udmamodes & 0x02)
---
 > 	if (ap->udmamodes & 0x02  &&  ata_dma_limit >= 1)