[PATCH v2 1/2] nvme: Add Arbitration Burst support

[Baolin Wang <baolin.wang@linux.alibaba.com>]

From the NVMe spec, "In order to make efficient use of the non-volatile
memory, it is often advantageous to execute multiple commands from a
Submission Queue in parallel. For Submission Queues that are using
weighted round robin with urgent priority class or round robin
arbitration, host software may configure an Arbitration Burst setting".
Thus add Arbitration Burst setting support.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 drivers/nvme/host/core.c | 29 +++++++++++++++++++++++++++++
 drivers/nvme/host/nvme.h |  1 +
 include/linux/nvme.h     |  1 +
 3 files changed, 31 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index c2c5bc4..f5f882f 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -61,6 +61,10 @@
 module_param(streams, bool, 0644);
 MODULE_PARM_DESC(streams, "turn on support for Streams write directives");
 
+static bool use_rab;
+module_param(use_rab, bool, 0644);
+MODULE_PARM_DESC(use_rab, "use controller's recommended arbitration burst");
+
 /*
  * nvme_wq - hosts nvme related works that are not reset or delete
  * nvme_reset_wq - hosts nvme reset works
@@ -1241,6 +1245,28 @@ int nvme_set_queue_count(struct nvme_ctrl *ctrl, int *count)
 }
 EXPORT_SYMBOL_GPL(nvme_set_queue_count);
 
+static void nvme_set_arbitration_burst(struct nvme_ctrl *ctrl)
+{
+	u32 result;
+	int status;
+
+	if (!use_rab || !ctrl->rab)
+		return;
+
+	/*
+	 * The Arbitration Burst setting indicates the maximum number of
+	 * commands that the controller may launch at one time from a
+	 * particular Submission Queue. It is recommended that host software
+	 * configure the Arbitration Burst setting as close to the recommended
+	 * value by the controller as possible.
+	 */
+	status = nvme_set_features(ctrl, NVME_FEAT_ARBITRATION,
+				   ctrl->rab & NVME_FEAT_ARBITRATION_MASK,
+				   NULL, 0, &result);
+	if (status)
+		dev_warn(ctrl->device, "Failed to set Arbitration Burst\n");
+}
+
 #define NVME_AEN_SUPPORTED \
 	(NVME_AEN_CFG_NS_ATTR | NVME_AEN_CFG_FW_ACT | \
 	 NVME_AEN_CFG_ANA_CHANGE | NVME_AEN_CFG_DISC_CHANGE)
@@ -2953,6 +2979,9 @@ int nvme_init_identify(struct nvme_ctrl *ctrl)
 	} else
 		ctrl->shutdown_timeout = shutdown_timeout;
 
+	ctrl->rab = id->rab;
+	nvme_set_arbitration_burst(ctrl);
+
 	ctrl->npss = id->npss;
 	ctrl->apsta = id->apsta;
 	prev_apst_enabled = ctrl->apst_enabled;
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index c0f4226..bc424c5 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -246,6 +246,7 @@ struct nvme_ctrl {
 	u16 kas;
 	u8 npss;
 	u8 apsta;
+	u8 rab;
 	u16 wctemp;
 	u16 cctemp;
 	u32 oaes;
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index 5ce51ab..fa629c8 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -909,6 +909,7 @@ enum {
 	NVME_SQ_PRIO_MEDIUM	= (2 << 1),
 	NVME_SQ_PRIO_LOW	= (3 << 1),
 	NVME_FEAT_ARBITRATION	= 0x01,
+	NVME_FEAT_ARBITRATION_MASK = 0x7,
 	NVME_FEAT_POWER_MGMT	= 0x02,
 	NVME_FEAT_LBA_RANGE	= 0x03,
 	NVME_FEAT_TEMP_THRESH	= 0x04,
-- 
1.8.3.1