IDE Floppy support for IOMEGA Zip Drive broken in 3.16 -> 3.17 transition

[Sergio Callegari <sergio.callegari@gmail.com>]

Hi,

I have an Iomega IDE Zip drive as in:

/dev/sda:

 Model=IOMEGA  ZIP 100       ATAPI       Floppy, FwRev=12.A, SerialNo=
 Config={ SpinMotCtl Removeable nonMagnetic }
 RawCHS=0/0/0, TrkSize=0, SectSize=0, ECCbytes=0
 BuffType=unknown, BuffSize=unknown, MaxMultSect=0
 (maybe): CurCHS=0/0/0, CurSects=0, LBA=yes, LBAsects=0
 IORDY=on/off, tPIO={min:500,w/IORDY:180}
 PIO modes:  pio0 pio1 pio2 pio3 
 AdvancedPM=no

 * signifies the current active mode


ATAPI Direct-access device, with removable media
        Model Number:       IOMEGA  ZIP 100       ATAPI       Floppy
        Serial Number:      
        Firmware Revision:  12.A    
Standards:
        Likely used: 4
Configuration:
        DRQ response: <=10ms with INTRQ
        Packet size: 12 bytes
        cache/buffer size  = unknown
Capabilities:
        LBA, IORDY(can be disabled)
        DMA: not supported
        PIO: pio0 pio1 pio2 pio3 
             Cycle time: no flow control=500ns  IORDY flow control=180ns
                Removable Media Status Notification feature set supported
Security: 
                supported
                enabled
        not     locked
        not     frozen
        not     expired: security count                                    
                                    
                supported: enhanced erase                                  
                                    
        Security level high   

The drive used to work just fine up to 3.16.  After a kernel upgrade, the
drive started giving issues.  Some checks let me be sure that the issue does
not exist with 3.16 and exists with 3.17.

The problem manifests with IOWAIT all of a sudden jumping high (approx 50%)
and staying high, even with the Iomega Zip drive unmounted. When this
happens any activity having to do with the drive hangs (even hdparm -i
/dev/sda). No related message in syslog apart from the indication of hung
processes. Detaching the drive makes the machine behave properly.

What has changed wrt IDE in 3.16->3.17 transition? Why is the issue present
even when the drive is not used (unmounted)?  How can I help diagnosing?