[PATCHv2 6/7] nvme: export controller reset event count via sysfs

[Nilay Shroff <nilay@linux.ibm.com>]

The NVMe controller transitions into the RESETTING state during error
recovery, link instability, firmware activation, or when a reset is
explicitly triggered by the user.

Expose a controller reset event count via sysfs to provide visibility
into these RESETTING state transitions. Observing the frequency of reset
events can help users identify issues such as PCIe errors or unstable
fabric links.

This counter can also be consumed by monitoring tools such as nvme-top
to improve controller-level observability.

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
---
 drivers/nvme/host/core.c  |  1 +
 drivers/nvme/host/nvme.h  |  1 +
 drivers/nvme/host/sysfs.c | 10 ++++++++++
 3 files changed, 12 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 11eb28117501..36af86515cb7 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -591,6 +591,7 @@ bool nvme_change_ctrl_state(struct nvme_ctrl *ctrl,
 		case NVME_CTRL_NEW:
 		case NVME_CTRL_LIVE:
 			changed = true;
+			ctrl->nr_reset = size_add(ctrl->nr_reset, 1);
 			fallthrough;
 		default:
 			break;
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index b1ce2857899a..5d90e5fa7298 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -360,6 +360,7 @@ struct nvme_ctrl {
 	struct work_struct fw_act_work;
 	unsigned long events;
 	size_t errors;
+	size_t nr_reset;
 #ifdef CONFIG_NVME_MULTIPATH
 	/* asymmetric namespace access: */
 	u8 anacap;
diff --git a/drivers/nvme/host/sysfs.c b/drivers/nvme/host/sysfs.c
index c1e2b93f7ae8..7958fe998139 100644
--- a/drivers/nvme/host/sysfs.c
+++ b/drivers/nvme/host/sysfs.c
@@ -658,6 +658,15 @@ static ssize_t nvme_adm_errors_show(struct device *dev,
 struct device_attribute dev_attr_adm_errors =
 	__ATTR(command_error_count, 0444, nvme_adm_errors_show, NULL);
 
+static ssize_t reset_events_show(struct device *dev,
+		   struct device_attribute *attr, char *buf)
+{
+	struct nvme_ctrl *ctrl = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%lu\n", ctrl->nr_reset);
+}
+static DEVICE_ATTR_RO(reset_events);
+
 #ifdef CONFIG_NVME_HOST_AUTH
 static ssize_t nvme_ctrl_dhchap_secret_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
@@ -805,6 +814,7 @@ static struct attribute *nvme_dev_attrs[] = {
 #endif
 	&dev_attr_adm_passthru_err_log_enabled.attr,
 	&dev_attr_adm_errors.attr,
+	&dev_attr_reset_events.attr,
 	NULL
 };
 
-- 
2.52.0