On Tuesday 23 June 2009 16:58:54 Frans Pop wrote:
> On Tuesday 23 June 2009, you wrote:
> > We might need to bisect this one. But Frans, just for the record
> > could you simply test reverting just that hunk? Thanks!
>
> I'm way ahead of you :-)
>
> Instead of a bisect [1] I decided to first see if some printks in both .26
> and .31 would show anything useful.
>
> With 2.6.31 and code included below I get:
> hda: ST34342A, ATA DISK drive
> FJP: id_dma_bug 0x7: &4: 0x0-0x4 no error
> hda: MWDMA2 mode selected
> hdc: Maxtor 6E040L0, ATA DISK drive
> hdd: CD-ROM 56X/AKH, ATAPI CD/DVD-ROM drive
> hdc: host max PIO5 wanted PIO255(auto-tune) selected PIO4
> FJP: ID_FIELD_VALID: 0x7 (true)
> FJP: id_dma_bug 0x7: &4: 0x0-0x4 no error
> hdc: MWDMA2 mode selected
> hdd: host max PIO5 wanted PIO255(auto-tune) selected PIO4
> FJP: ID_FIELD_VALID: 0x2 (true)
> FJP: id_dma_bug 0x2: &2: 0x1-0x1 bad modes <-------------
> hdd: bad DMA info in identify block
>
> Note that this included a complete revert of 8d64fcd9 (with minor conflict
> resolved).
>
> Here's the same output with 2.6.26.3 with equivalent debug statements:
> hda: ST34342A, ATA DISK drive
> FJP: id_dma_bug 0x7: &4: 0x0-0x0 no error
> hda: MWDMA2 mode selected
> hdc: Maxtor 6E040L0, ATA DISK drive
> hdd: CD-ROM 56X/AKH, ATAPI CD/DVD-ROM drive
> FJP: id_dma_bug 0x7: &4: 0x0-0x0 no error
> hdc: MWDMA2 mode selected
> FJP: id_dma_bug 0x2: &2: 0x0-0x0 no error <-------------
> hdd: MWDMA2 mode selected
>
> So it seems to me that in 2.6.26 something was broken in the way these ID
> fields were handled, at least in this check. This is now fixed (possibly
Great debugging work, thanks!
> by the changes around 5b90e990..48fb2688) and *that* causes the
> regression. Note that the hard disks are also affected.
I see it now -- in commit c419993 ("ide-iops: only clear DMA words
on setting DMA mode") we fixed a bug in ide_config_drive_speed()..
[ It was a real bug resulting in incorrect data being passed to
the user-space through HDIO_GET_IDENTITY ioctl ('hdparm -i'). ]
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