scsi: ufs: Avoid busy-waiting by eliminating tag conflicts

Instead of tracking which tags are in use in the ufs_hba.lrb_in_use
bitmask, rely on the block layer tag allocation mechanism. This patch
removes the following busy-waiting loop if ufshcd_issue_devman_upiu_cmd()
and the block layer accidentally allocate the same tag for a SCSI request:

 * ufshcd_queuecommand() returns SCSI_MLQUEUE_HOST_BUSY.

 * The SCSI core requeues the SCSI command.

Cc: Can Guo <cang@codeaurora.org>
Cc: Stanley Chu <stanley.chu@mediatek.com>
Cc: Avri Altman <avri.altman@wdc.com>
Cc: Tomas Winkler <tomas.winkler@intel.com>
Link: https://lore.kernel.org/r/20191209181309.196233-2-bvanassche@acm.org
Tested-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 2 insertions, 4 deletions

diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
index 2740f6941ec6..56b9da6db1cc 100644
--- a/drivers/scsi/ufs/ufshcd.h
+++ b/drivers/scsi/ufs/ufshcd.h
@@ -212,13 +212,11 @@ struct ufs_query {
  * @type: device management command type - Query, NOP OUT
  * @lock: lock to allow one command at a time
  * @complete: internal commands completion
- * @tag_wq: wait queue until free command slot is available
  */
 struct ufs_dev_cmd {
 	enum dev_cmd_type type;
 	struct mutex lock;
 	struct completion *complete;
-	wait_queue_head_t tag_wq;
 	struct ufs_query query;
 };
 
@@ -483,7 +481,7 @@ struct ufs_stats {
  * @host: Scsi_Host instance of the driver
  * @dev: device handle
  * @lrb: local reference block
- * @lrb_in_use: lrb in use
+ * @cmd_queue: Used to allocate command tags from hba->host->tag_set.
  * @outstanding_tasks: Bits representing outstanding task requests
  * @outstanding_reqs: Bits representing outstanding transfer requests
  * @capabilities: UFS Controller Capabilities
@@ -541,6 +539,7 @@ struct ufs_hba {
 
 	struct Scsi_Host *host;
 	struct device *dev;
+	struct request_queue *cmd_queue;
 	/*
 	 * This field is to keep a reference to "scsi_device" corresponding to
 	 * "UFS device" W-LU.
@@ -561,7 +560,6 @@ struct ufs_hba {
 	u32 ahit;
 
 	struct ufshcd_lrb *lrb;
-	unsigned long lrb_in_use;
 
 	unsigned long outstanding_tasks;
 	unsigned long outstanding_reqs;