ATAPI DMA timeouts showing up in logs

Now that I've got the proper IDE driver in place (2.4.20rc4) and the master drive on the primary interface is running at a full ATA133, these have started showing up in the logs - 2 or 3 a day:

hdc: timeout waiting for DMA
ide_dmaproc: chipset supported ide_dma_timeout func only: 14
hdc: status timeout: status=0xd0 { Busy }
hdc: drive not ready for command
hdc: ATAPI reset complete

Here's the dmesg output about this drive:

Uniform Multi-Platform E-IDE driver Revision: 6.31
ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx

VP_IDE: IDE controller on PCI bus 00 dev 89
PCI: No IRQ known for interrupt pin A of device 00:11.1.
VP_IDE: chipset revision 6
VP_IDE: not 100% native mode: will probe irqs later
ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx

VP_IDE: VIA vt8235 (rev 00) IDE UDMA133 controller on pci00:11.1

    ide0: BM-DMA at 0xb800-0xb807, BIOS settings: hda:DMA, hdb:pio
    ide1: BM-DMA at 0xb808-0xb80f, BIOS settings: hdc:DMA, hdd:pio

hda: Maxtor 6E030L0, ATA DISK drive
hdc: 56X CD-ROM, ATAPI CD/DVD-ROM drive
ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
ide1 at 0x170-0x177,0x376 on irq 15
blk: queue c034b164, I/O limit 4095Mb (mask 0xffffffff)
hda: 60058656 sectors (30750 MB) w/2048KiB Cache, CHS=3738/255/63, UDMA(133)

hdc: ATAPI 52X CD-ROM drive, 128kB Cache, UDMA(33) Uniform CD-ROM driver Revision: 3.12

And /sbin/hdparm -I /dev/hdc

/dev/hdc:

ATAPI CD-ROM, with removable media

        Model Number:       56X CD-ROM
        Serial Number:      MT1102A Firmware
        Firmware Revision:  VER 1.5F

Standards:
Used: ATAPI for CD-ROMs, SFF-8020i, r2.5
Supported: CD-ROM ATAPI-2
Configuration:
DRQ response: 50us.
Packet size: 12 bytes
Capabilities:
LBA, IORDY(cannot be disabled)
DMA: *mdma0 mdma1 mdma2 *udma0 udma1 udma2 (?)
Cycle time: min=120ns recommended=150ns
PIO: pio0 pio1 pio2 pio3 pio4
Cycle time: no flow control=227ns IORDY flow control=120ns

And /sbin/hdparm -i /dev/hdc

/dev/hdc:

Model=56X CD-ROM, FwRev=VER 1.5F, SerialNo=MT1102A Firmware Config={ Fixed Removeable DTR<=5Mbs DTR>10Mbs nonMagnetic } RawCHS=0/0/0, TrkSize=0, SectSize=0, ECCbytes=0 BuffType=unknown, BuffSize=0kB, MaxMultSect=0 (maybe): CurCHS=0/0/0, CurSects=0, LBA=yes, LBAsects=0 IORDY=yes, tPIO={min:227,w/IORDY:120}, tDMA={min:120,rec:150} PIO modes: pio0 pio1 pio2 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 *udma2
AdvancedPM=no

And finally,

/sbin/hdparm -v /dev/hdc

/dev/hdc:
HDIO_GET_MULTCOUNT failed: Invalid argument

 IO_support   =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  1 (on)
 readahead    =  8 (on)

HDIO_GETGEO failed: Invalid argument

This last one is the only indication that something might be amiss - the two instances of "invalid argument" Other than that, the drive appears to work just fine.

What am I looking at?

DG

My guess is its the IDE command/DMA sequence bug that Khalid fixed in -ac. Some drives also take a very long time on retrying blocks and that might cause a timeout/reset too.

Those are ones CD-ROM's dont support