dmaengine: idxd: Add wq occupancy information to sysfs attribute

Add occupancy information to wq sysfs attribute. Attribute will show
wq occupancy data if "WQ Occupancy Support" field in WQCAP is 1. It
displays the number of entries currently in this WQ. This is provided
as an estimate and should not be relied on to determine whether there
is space in the WQ. The data is to provide information to user apps
for flow control.
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/162275745546.1857062.8765615879420582018.stgit@djiang5-desk3.ch.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/ABI/stable/sysfs-driver-dma-idxd

@@ -211,6 +211,13 @@ Contact:	dmaengine@vger.kernel.org
 Description:	Indicate whether ATS disable is turned on for the workqueue.
 		0 indicates ATS is on, and 1 indicates ATS is off for the workqueue.
 
+What:		/sys/bus/dsa/devices/wq<m>.<n>/occupancy
+Date		May 25, 2021
+KernelVersion:	5.14.0
+Contact:	dmaengine@vger.kernel.org
+Description:	Show the current number of entries in this WQ if WQ Occupancy
+		Support bit WQ capabilities is 1.
+
 What:           /sys/bus/dsa/devices/engine<m>.<n>/group_id
 Date:           Oct 25, 2019
 KernelVersion:  5.6.0

drivers/dma/idxd/registers.h

@@ -349,6 +349,9 @@ union wqcfg {
 } __packed;
 
 #define WQCFG_PASID_IDX                2
+#define WQCFG_OCCUP_IDX		6
+
+#define WQCFG_OCCUP_MASK	0xffff
 
 /*
  * This macro calculates the offset into the WQCFG register

drivers/dma/idxd/sysfs.c

@@ -1246,6 +1246,24 @@ static ssize_t wq_ats_disable_store(struct device *dev, struct device_attribute
 static struct device_attribute dev_attr_wq_ats_disable =
 		__ATTR(ats_disable, 0644, wq_ats_disable_show, wq_ats_disable_store);
 
+static ssize_t wq_occupancy_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct idxd_wq *wq = confdev_to_wq(dev);
+	struct idxd_device *idxd = wq->idxd;
+	u32 occup, offset;
+
+	if (!idxd->hw.wq_cap.occupancy)
+		return -EOPNOTSUPP;
+
+	offset = WQCFG_OFFSET(idxd, wq->id, WQCFG_OCCUP_IDX);
+	occup = ioread32(idxd->reg_base + offset) & WQCFG_OCCUP_MASK;
+
+	return sysfs_emit(buf, "%u\n", occup);
+}
+
+static struct device_attribute dev_attr_wq_occupancy =
+		__ATTR(occupancy, 0444, wq_occupancy_show, NULL);
+
 static struct attribute *idxd_wq_attributes[] = {
 	&dev_attr_wq_clients.attr,
 	&dev_attr_wq_state.attr,
@@ -1261,6 +1279,7 @@ static struct attribute *idxd_wq_attributes[] = {
 	&dev_attr_wq_max_transfer_size.attr,
 	&dev_attr_wq_max_batch_size.attr,
 	&dev_attr_wq_ats_disable.attr,
+	&dev_attr_wq_occupancy.attr,
 	NULL,
 };