USB: mass storage: emulation of sat scsi_pass_thru with ATACB

I have got a cypress usb-ide bridge and I would like to tune or monitor
my disk with tools like hdparm, hddtemp or smartctl.

My controller support a way to send raw ATA command to the disk with
something call atacb (see
http://download.cypress.com.edgesuite.net/design_resources/datasheets/contents/cy7c68300c_8.pdf).

Atacb support can be added for each application, but there is some disadvantages :
- all application need to be patched
- A race is possible if there other accesses, because the emulation can
be split in 2 atacb scsi transactions. One for sending the command, one
for reading the register (if ck_cond is set). 

I have implemented the emulation in usb-storage with a special proto_handler,
and an unsual entry.

Signed-off-by: Matthieu CASTET <castet.matthieu@free.fr>
Signed-off-by: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/storage/unusual_devs.h

@@ -1719,6 +1719,14 @@ UNUSUAL_DEV(  0xed06, 0x4500, 0x0001, 0x0001,
 		US_SC_DEVICE, US_PR_DEVICE, NULL,
 		US_FL_CAPACITY_HEURISTICS),
 
+#ifdef CONFIG_USB_STORAGE_CYPRESS_ATACB
+UNUSUAL_DEV(  0x04b4, 0x6830, 0x0000, 0x9999,
+		"Cypress",
+		"Cypress AT2LP",
+		US_SC_CYP_ATACB, US_PR_BULK, NULL,
+		0),
+#endif
+
 /* Control/Bulk transport for all SubClass values */
 USUAL_DEV(US_SC_RBC, US_PR_CB, USB_US_TYPE_STOR),
 USUAL_DEV(US_SC_8020, US_PR_CB, USB_US_TYPE_STOR),