From: Xiang Chen <chenxiang66@hisilicon.com>
Date: Mon, 21 May 2018 18:09:14 +0800
Subject: scsi: hisi_sas: change slot index allocation mode
Git-commit: fa3be0f23139ddc4dffbfdef6bbd118e30dfcafe
Patch-mainline: v4.18-rc1
References: FATE#326253

Currently we find the lowest available empty bit in the IPTT bitmap to
allocate the IPTT for a command.

To reduce possibility of hitting unknown SoC bugs and also aid in the
debugging of those same bugs, change the allocation mode.

The next allocation method is to use the next free slot adjacent to the
most recently allocated slot, in a round-robin fashion.

Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Johannes Thumshirn <jthumshirn@suse.de>
---
 drivers/scsi/hisi_sas/hisi_sas.h      |  1 +
 drivers/scsi/hisi_sas/hisi_sas_main.c | 13 ++++++++++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/hisi_sas/hisi_sas.h b/drivers/scsi/hisi_sas/hisi_sas.h
index 52fc709dd862..3c8840089cd5 100644
--- a/drivers/scsi/hisi_sas/hisi_sas.h
+++ b/drivers/scsi/hisi_sas/hisi_sas.h
@@ -274,6 +274,7 @@ struct hisi_hba {
 	struct workqueue_struct *wq;
 
 	int slot_index_count;
+	int last_slot_index;
 	unsigned long *slot_index_tags;
 	unsigned long reject_stp_links_msk;
 
diff --git a/drivers/scsi/hisi_sas/hisi_sas_main.c b/drivers/scsi/hisi_sas/hisi_sas_main.c
index 66388741e73c..796fdfc73c75 100644
--- a/drivers/scsi/hisi_sas/hisi_sas_main.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_main.c
@@ -195,11 +195,18 @@ static int hisi_sas_slot_index_alloc(struct hisi_hba *hisi_hba, int *slot_idx)
 	unsigned int index;
 	void *bitmap = hisi_hba->slot_index_tags;
 
-	index = find_first_zero_bit(bitmap, hisi_hba->slot_index_count);
-	if (index >= hisi_hba->slot_index_count)
-		return -SAS_QUEUE_FULL;
+	index = find_next_zero_bit(bitmap, hisi_hba->slot_index_count,
+			hisi_hba->last_slot_index + 1);
+	if (index >= hisi_hba->slot_index_count) {
+		index = find_next_zero_bit(bitmap, hisi_hba->slot_index_count,
+					   0);
+		if (index >= hisi_hba->slot_index_count)
+			return -SAS_QUEUE_FULL;
+	}
 	hisi_sas_slot_index_set(hisi_hba, index);
 	*slot_idx = index;
+	hisi_hba->last_slot_index = index;
+
 	return 0;
 }