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From
SubjectFw: UDMA on 815e chipset
Date
Greetings Gurus,

Have I found a tiny, perhaps irrelevant, bug ?

I have recently installed SuSE 7.0 with the supplied 2.2.16 kernel on my
homebuilt dual-boot machine, which has an 815e chipset (Asus CuSL2 board), plus
30GB IBM Deskstar 75GXP HDD (hda). As I understand it both of these support UDMA modes4 and 5 / ATA 66 and 100.

The bios will not allow UDMA mode 5 to be set unless the correct cable is
detected. At boot-time under Windows the bios reports that UDMA Mode 5
has been set.

I decided to tweak the HDD performance under linux. I began with ATA 33 by adding the following to my boot.local : /sbin/hdparm -c1 -m16 -d1 -X66 /dev/hda

This line causes no problems and hparm reports UDMA mode 2 set with cache reads at 139.13 MB/sec and disk reads at 12.87 MB/sec.

I then try increasing to ATA 66 by substituting -X68 for X66.

At linux boot-time I now see that XF68 has been set, but then I see the error
message : "ide0: speed warning UDMA /3/4/5 is not functional". As I understand it, this means that the kernel has tested for the correct cable, but sees a negative response.

Even though I see the error message, I think that UDMA 4 / ATA 66 must actually have been set, because hdparm now reports cache reads at 143.82 MB/sec and disk reads at 15.76 MB/Ssec. hdparm also reports that the HDD is in UDMA mode 4.

Much the same thing happens if I try for ATA 100 / UDMA 5 by substituting -X69. hdparm now reports that the drive is in UDMA mode 5, but I do not see any improvement in transfer speeds, from which I assume that my kernel cannot go higher than ATA 66.

I assume (unwisely ?), from all this that for some reason the kernel's
check for the correct UDMA cabling on this chipset / motherboard is
failing, but that it is actually succeding in setting UDMA mode 5 and is happily running at ATA 66. Hence my "possibly irrelevant" bug report.

I have carried out all of the tests I mention above with a substitute cable, but the results are the same. I have not (yet) suffered any loss of data or other problems by ignoring the speed warning.

I am not subscribed to this list (perhaps I have revealed enough ignorance
above to explain why not), but I do not know where else I should report
the "problem", or where else I might get some feedback. If anyone can be
bothered to respond, then I would be very grateful if you could CC the reply
to me.

Thanks

Geoff

"Scattered we were when the long night was breaking:
But in bright morning converse again"

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