start stop libata attached SATA disks, take 2

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Jeff,
Here is another (more successful) attempt at that patch.

ChangeLog:
- adds minimal START STOP UNIT SCSI command functionality to libata (follows sat-r05 apart from the IMMED bit).
- implements the TEST UNIT READY SCSI command as indicated

    by sat-r05.

Patch against lk 2.6.13-rc5 .

Tested on my ST380013AS Seagate SATA disk with a Sil 3112 HBA. Stop (spin down [enter standby power mode]) seems to work as does start. Start takes 3.8 seconds to spin up on my disk. TEST UNIT READY works returning GOOD status (after 0 ms) when the disk is active or idle and the "initializing command required" sense (after 180 ms) when the disk is in standby power mode.

I looked a bit closer at the power condition states in SBC-2 and I assume there is an equivalence with SATA disks:

State Disk mechanics
- ----------------------------------

Active   Spinning, heads on track
Idle     Spinning, heads parked
Standby  Spun down,  " "
Stop     Spun down,  " "

The difference between "standby" and "stop" is that an initializing command is required (i.e. START STOP UNIT command, start=1) to transition out of "stop" state (but not "standby"). As far as I can see ATA disks don't have a "stop" state that can be accessed via the ATA command set so the the SAT draft says to translate a SCSI START STOP UNIT command, start=0 (i.e. stop) into SATA disk being placed into standby mode. That is fine but a SATA (and PATA) disk doesn't need an initializing command to go into active state, any media access command will do that. This is all fine, I just find it a little curious what SAT is defining should happen for the TEST UNIT READY translation.

Doug Gilbert

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@@ -108,6 +108,8 @@
 
 	/* ATA device commands */
 	ATA_CMD_CHK_POWER	= 0xE5, /* check power mode */
+	ATA_CMD_STANDBY		= 0xE2, /* place in standby power mode */
+	ATA_CMD_IDLE		= 0xE3, /* place in idle power mode */
 	ATA_CMD_EDD		= 0x90,	/* execute device diagnostic */
 	ATA_CMD_FLUSH		= 0xE7,
 	ATA_CMD_FLUSH_EXT	= 0xEA,

Looks pretty decent, however...

Can you please resend as two patches:

#1: implement START STOP UNIT
#2: implement TEST UNIT READY

I need to think about TUR a bit more. Separating into two patches would allow me to apply SSU patch to upstream immediately, while applying the TUR feature to libata-dev.git respository, queueing it for further review and eventual upstream merge.

Jeff