NVMe: Avoid shift operation when writing cq head doorbell

Changes the type of dev->db_stride to unsigned and changes the value
stored there to be 1 << the current value. Then there is less
calculation to be done at completion time.

Signed-off-by: Haiyan Hu <huhaiyan@huawei.com>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>

2 files changed, 6 insertions, 6 deletions

diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c
index 26d03fa0bf26..073aec913c78 100644
--- a/drivers/block/nvme-core.c
+++ b/drivers/block/nvme-core.c
@@ -775,7 +775,7 @@ static int nvme_process_cq(struct nvme_queue *nvmeq)
         if (head == nvmeq->cq_head && phase == nvmeq->cq_phase)
                 return 0;
 
-        writel(head, nvmeq->q_db + (1 << nvmeq->dev->db_stride));
+        writel(head, nvmeq->q_db + nvmeq->dev->db_stride);
         nvmeq->cq_head = head;
         nvmeq->cq_phase = phase;
 
@@ -1113,7 +1113,7 @@ static struct nvme_queue *nvme_alloc_queue(struct nvme_dev *dev, int qid,
         init_waitqueue_head(&nvmeq->sq_full);
         init_waitqueue_entry(&nvmeq->sq_cong_wait, nvme_thread);
         bio_list_init(&nvmeq->sq_cong);
-        nvmeq->q_db = &dev->dbs[qid << (dev->db_stride + 1)];
+        nvmeq->q_db = &dev->dbs[qid * 2 * dev->db_stride];
         nvmeq->q_depth = depth;
         nvmeq->cq_vector = vector;
         nvmeq->q_suspended = 1;
@@ -1149,7 +1149,7 @@ static void nvme_init_queue(struct nvme_queue *nvmeq, u16 qid)
         nvmeq->sq_tail = 0;
         nvmeq->cq_head = 0;
         nvmeq->cq_phase = 1;
-        nvmeq->q_db = &dev->dbs[qid << (dev->db_stride + 1)];
+        nvmeq->q_db = &dev->dbs[qid * 2 * dev->db_stride];
         memset(nvmeq->cmdid_data, 0, extra);
         memset((void *)nvmeq->cqes, 0, CQ_SIZE(nvmeq->q_depth));
         nvme_cancel_ios(nvmeq, false);
@@ -1741,7 +1741,7 @@ static int set_queue_count(struct nvme_dev *dev, int count)
 
 static size_t db_bar_size(struct nvme_dev *dev, unsigned nr_io_queues)
 {
-        return 4096 + ((nr_io_queues + 1) << (dev->db_stride + 3));
+        return 4096 + ((nr_io_queues + 1) * 8 * dev->db_stride);
 }
 
 static int nvme_setup_io_queues(struct nvme_dev *dev)
@@ -1958,7 +1958,7 @@ static int nvme_dev_map(struct nvme_dev *dev)
         if (!dev->bar)
                 goto disable;
 
-        dev->db_stride = NVME_CAP_STRIDE(readq(&dev->bar->cap));
+        dev->db_stride = 1 << NVME_CAP_STRIDE(readq(&dev->bar->cap));
         dev->dbs = ((void __iomem *)dev->bar) + 4096;
 
         return 0;
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index 26ebcf41c213..8119a476cb29 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -80,7 +80,7 @@ struct nvme_dev {
         struct dma_pool *prp_small_pool;
         int instance;
         int queue_count;
-        int db_stride;
+        u32 db_stride;
         u32 ctrl_config;
         struct msix_entry *entry;
         struct nvme_bar __iomem *bar;