linux-kernel - [PATCH 4.4 096/192] [PATCH 100/135] cxlflash: Fix to avoid unnecessary scan with internal LUNs

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Message-Id: <20160912152202.966835764@linuxfoundation.org>
Date:   Mon, 12 Sep 2016 19:00:05 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Manoj N. Kumar" <manoj@...ux.vnet.ibm.com>,
        "Matthew R. Ochs" <mrochs@...ux.vnet.ibm.com>,
        Uma Krishnan <ukrishn@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.4 096/192] [PATCH 100/135] cxlflash: Fix to avoid unnecessary scan with internal LUNs

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 603ecce95f4817074a724a889cd88c3c8210f933 ]

When switching to the internal LUN defined on the
IBM CXL flash adapter, there is an unnecessary
scan occurring on the second port. This scan leads
to the following extra lines in the log:

Dec 17 10:09:00 tul83p1 kernel: [ 3708.561134] cxlflash 0008:00:00.0: cxlflash_queuecommand: (scp=c0000000fc1f0f00) 11/1/0/0 cdb=(A0000000-00000000-10000000-00000000)
Dec 17 10:09:00 tul83p1 kernel: [ 3708.561147] process_cmd_err: cmd failed afu_rc=32 scsi_rc=0 fc_rc=0 afu_extra=0xE, scsi_extra=0x0, fc_extra=0x0

By definition, both of the internal LUNs are on the first port/channel.

When the lun_mode is switched to internal LUN the
same value for host->max_channel is retained. This
causes an unnecessary scan over the second port/channel.

This fix alters the host->max_channel to 0 (1 port), if internal
LUNs are configured and switches it back to 1 (2 ports) while
going back to external LUNs.

Signed-off-by: Manoj N. Kumar <manoj@...ux.vnet.ibm.com>
Acked-by: Matthew R. Ochs <mrochs@...ux.vnet.ibm.com>
Reviewed-by: Uma Krishnan <ukrishn@...ux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/scsi/cxlflash/main.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/drivers/scsi/cxlflash/main.c
+++ b/drivers/scsi/cxlflash/main.c
@@ -2149,6 +2149,16 @@ static ssize_t lun_mode_store(struct dev
 	rc = kstrtouint(buf, 10, &lun_mode);
 	if (!rc && (lun_mode < 5) && (lun_mode != afu->internal_lun)) {
 		afu->internal_lun = lun_mode;
+
+		/*
+		 * When configured for internal LUN, there is only one channel,
+		 * channel number 0, else there will be 2 (default).
+		 */
+		if (afu->internal_lun)
+			shost->max_channel = 0;
+		else
+			shost->max_channel = NUM_FC_PORTS - 1;
+
 		afu_reset(cfg);
 		scsi_scan_host(cfg->host);
 	}