[SCSI] sd: pause in sd_spinup_disk for slow USB devices

This patch adds a delay tailored for USB flash devices that are slow to
initialize their firmware.  The symptom is a repeated Unit Attention with
ASC=0x28 (Not Ready to Ready transition).  The patch will wait for up to 5
seconds for such devices to become ready.  Normal devices won't send the
repeated Unit Attention sense key and hence won't trigger the patch.

This fixes a problem with James Roberts-Thomson's USB device, and I've
seen several reports of other devices exhibiting the same symptoms --
presumably they will be helped as well.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/sd.c

@@ -984,7 +984,7 @@ static void
 sd_spinup_disk(struct scsi_disk *sdkp, char *diskname,
 	       struct scsi_request *SRpnt, unsigned char *buffer) {
 	unsigned char cmd[10];
-	unsigned long spintime_value = 0;
+	unsigned long spintime_expire = 0;
 	int retries, spintime;
 	unsigned int the_result;
 	struct scsi_sense_hdr sshdr;
@@ -1071,12 +1071,27 @@ sd_spinup_disk(struct scsi_disk *sdkp, char *diskname,
 				scsi_wait_req(SRpnt, (void *)cmd, 
 					      (void *) buffer, 0/*512*/, 
 					      SD_TIMEOUT, SD_MAX_RETRIES);
-				spintime_value = jiffies;
+				spintime_expire = jiffies + 100 * HZ;
+				spintime = 1;
 			}
-			spintime = 1;
 			/* Wait 1 second for next try */
 			msleep(1000);
 			printk(".");
+
+		/*
+		 * Wait for USB flash devices with slow firmware.
+		 * Yes, this sense key/ASC combination shouldn't
+		 * occur here.  It's characteristic of these devices.
+		 */
+		} else if (sense_valid &&
+				sshdr.sense_key == UNIT_ATTENTION &&
+				sshdr.asc == 0x28) {
+			if (!spintime) {
+				spintime_expire = jiffies + 5 * HZ;
+				spintime = 1;
+			}
+			/* Wait 1 second for next try */
+			msleep(1000);
 		} else {
 			/* we don't understand the sense code, so it's
 			 * probably pointless to loop */
@@ -1088,8 +1103,7 @@ sd_spinup_disk(struct scsi_disk *sdkp, char *diskname,
 			break;
 		}
 
-	} while (spintime &&
-		 time_after(spintime_value + 100 * HZ, jiffies));
+	} while (spintime && time_before_eq(jiffies, spintime_expire));
 
 	if (spintime) {
 		if (scsi_status_is_good(the_result))