[PATCH] sr.c should issue TEST_UNIT_READY

The linux/drivers/scsi/sr.c code will issue a MODE_SENSE[_10] command to
a device as the first command sent to the device.  If the device has
just come out of reset, it will likely respond with a UNIT_ATTENTION /
NOT_READY status, which causes the MODE_SENSE to fail.  In fact, the
device may have several UNIT_ATTENTION conditions queued up (power-up
reset, media change, etc.)

This results in the mode page 0x2a data not being properly read and
interpreted.  As an end-effect, things like packet-writing don't work
(because the writeable bit is not set).

The solution to this is to issue one or more TEST_UNIT_READY commands to
the device to clear any pending UNIT_ATTENTION conditions.  This is the
technique used by sd.c -- in fact, this code was lifted directly from
sd.c

At some point in the future, abstraction of this initial TEST_UNIT_READY
code between all high-level SCSI drivers may be apropriate.  For now,
this patch makes sr.c issue TEST_UNIT_READY to clear the UNIT_ATTENTION,
thus allowing the mode page 0x2a code to work properly.  Given the
approaching 2.6.0-final release, I urge that this patch be accepted.

drivers/scsi/sr.c

@@ -695,6 +695,10 @@ static void get_capabilities(struct scsi_cd *cd)
 	unsigned char *buffer;
 	int rc, n;
 	struct scsi_mode_data data;
+	struct scsi_request *SRpnt;
+	unsigned char cmd[MAX_COMMAND_SIZE];
+	unsigned int the_result;
+	int retries;
 
 	static char *loadmech[] =
 	{
@@ -708,11 +712,46 @@ static void get_capabilities(struct scsi_cd *cd)
 		""
 	};
 
+	/* allocate a request for the TEST_UNIT_READY */
+	SRpnt = scsi_allocate_request(cd->device);
+	if (!SRpnt) {
+		printk(KERN_WARNING "(get_capabilities:) Request allocation "
+		       "failure.\n");
+		return;
+	}
+
+	/* allocate transfer buffer */
 	buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
 	if (!buffer) {
 		printk(KERN_ERR "sr: out of memory.\n");
+		scsi_release_request(SRpnt);
 		return;
 	}
+
+	/* issue TEST_UNIT_READY until the initial startup UNIT_ATTENTION
+	 * conditions are gone, or a timeout happens
+	 */
+	retries = 0;
+	do {
+		memset((void *)cmd, 0, MAX_COMMAND_SIZE);
+		cmd[0] = TEST_UNIT_READY;
+
+		SRpnt->sr_cmd_len = 0;
+		SRpnt->sr_sense_buffer[0] = 0;
+		SRpnt->sr_sense_buffer[2] = 0;
+		SRpnt->sr_data_direction = DMA_NONE;
+
+		scsi_wait_req (SRpnt, (void *) cmd, buffer,
+			       0, SR_TIMEOUT, MAX_RETRIES);
+
+		the_result = SRpnt->sr_result;
+		retries++;
+	} while (retries < 5 && 
+		 (!scsi_status_is_good(the_result) ||
+		  ((driver_byte(the_result) & DRIVER_SENSE) &&
+		   SRpnt->sr_sense_buffer[2] == UNIT_ATTENTION)));
+
+	/* ask for mode page 0x2a */
 	rc = scsi_mode_sense(cd->device, 0, 0x2a, buffer, 128,
 			     SR_TIMEOUT, 3, &data);
 
@@ -722,6 +761,7 @@ static void get_capabilities(struct scsi_cd *cd)
 		cd->cdi.mask |= (CDC_CD_R | CDC_CD_RW | CDC_DVD_R |
 					 CDC_DVD | CDC_DVD_RAM |
 					 CDC_SELECT_DISC | CDC_SELECT_SPEED);
+		scsi_release_request(SRpnt);
 		kfree(buffer);
 		printk("%s: scsi-1 drive\n", cd->cdi.name);
 		return;
@@ -775,6 +815,7 @@ static void get_capabilities(struct scsi_cd *cd)
 	/*else    I don't think it can close its tray
 		cd->cdi.mask |= CDC_CLOSE_TRAY; */
 
+	scsi_release_request(SRpnt);
 	kfree(buffer);
 }