scsi: cxlflash: Support WS16 unmap

The cxlflash driver supports performing a write-same16 to scrub virtual
luns when they are released by a user. To date, AFUs for adapters that
are supported by cxlflash do not have the capability to unmap as part of
the WS operation. This can lead to fragmented flash devices which results
in performance degradation.

Future AFUs can optionally support unmap write-same commands and reflects
this support via the context control register. This provides userspace
applications with direct visibility such that they need not depend on a
host API.

Detect unmap support during cxlflash initialization by reading the context
control register associated with the primary hardware queue. Update the
existing write_same16() routine to set the unmap bit in the CDB when unmap
is supported by the host.

Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Uma Krishnan <ukrishn@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/cxlflash/common.h

@@ -147,6 +147,7 @@ struct cxlflash_cfg {
 	wait_queue_head_t tmf_waitq;
 	spinlock_t tmf_slock;
 	bool tmf_active;
+	bool ws_unmap;		/* Write-same unmap supported */
 	wait_queue_head_t reset_waitq;
 	enum cxlflash_state state;
 	async_cookie_t async_reset_cookie;

drivers/scsi/cxlflash/main.c

@@ -1812,6 +1812,18 @@ static int init_global(struct cxlflash_cfg *cfg)
 			SISL_CTX_CAP_AFU_CMD | SISL_CTX_CAP_GSCSI_CMD),
 			&hwq->ctrl_map->ctx_cap);
 	}
+
+	/*
+	 * Determine write-same unmap support for host by evaluating the unmap
+	 * sector support bit of the context control register associated with
+	 * the primary hardware queue. Note that while this status is reflected
+	 * in a context register, the outcome can be assumed to be host-wide.
+	 */
+	hwq = get_hwq(afu, PRIMARY_HWQ);
+	reg = readq_be(&hwq->host_map->ctx_ctrl);
+	if (reg & SISL_CTX_CTRL_UNMAP_SECTOR)
+		cfg->ws_unmap = true;
+
 	/* Initialize heartbeat */
 	afu->hb = readq_be(&afu->afu_map->global.regs.afu_hb);
 out:

drivers/scsi/cxlflash/sislite.h

@@ -283,6 +283,7 @@ struct sisl_host_map {
 	__be64 rrq_end;		/* write sequence: start followed by end */
 	__be64 cmd_room;
 	__be64 ctx_ctrl;	/* least significant byte or b56:63 is LISN# */
+#define SISL_CTX_CTRL_UNMAP_SECTOR	0x8000000000000000ULL /* b0 */
 	__be64 mbox_w;		/* restricted use */
 	__be64 sq_start;	/* Submission Queue (R/W): write sequence and */
 	__be64 sq_end;		/* inclusion semantics are the same as RRQ    */

drivers/scsi/cxlflash/vlun.c

@@ -446,6 +446,7 @@ static int write_same16(struct scsi_device *sdev,
 	while (left > 0) {
 
 		scsi_cmd[0] = WRITE_SAME_16;
+		scsi_cmd[1] = cfg->ws_unmap ? 0x8 : 0;
 		put_unaligned_be64(offset, &scsi_cmd[2]);
 		put_unaligned_be32(ws_limit < left ? ws_limit : left,
 				   &scsi_cmd[10]);