dmaengine: idxd: add support for configurable max wq xfer size

Add sysfs attribute max_xfer_size to wq in order to allow the max xfer
size configured on a per wq basis. Add support code to configure
the valid user input on wq enable. This is a performance tuning
parameter.
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/159865265404.29141.3049399618578194052.stgit@djiang5-desk3.ch.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

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

@@ -170,6 +170,13 @@ Contact:        dmaengine@vger.kernel.org
 Description:    The number of entries in this work queue that may be filled
 		via a limited portal.
 
+What:		/sys/bus/dsa/devices/wq<m>.<n>/max_transfer_size
+Date:		Aug 28, 2020
+KernelVersion:	5.10.0
+Contact:	dmaengine@vger.kernel.org
+Description:	The max transfer sized for this workqueue. Cannot exceed device
+		max transfer size. Configurable parameter.
+
 What:           /sys/bus/dsa/devices/engine<m>.<n>/group_id
 Date:           Oct 25, 2019
 KernelVersion:  5.6.0

drivers/dma/idxd/device.c

@@ -529,7 +529,7 @@ static int idxd_wq_config_write(struct idxd_wq *wq)
 	wq->wqcfg.priority = wq->priority;
 
 	/* bytes 12-15 */
-	wq->wqcfg.max_xfer_shift = idxd->hw.gen_cap.max_xfer_shift;
+	wq->wqcfg.max_xfer_shift = ilog2(wq->max_xfer_bytes);
 	wq->wqcfg.max_batch_shift = idxd->hw.gen_cap.max_batch_shift;
 
 	dev_dbg(dev, "WQ %d CFGs\n", wq->id);

drivers/dma/idxd/idxd.h

@@ -114,6 +114,7 @@ struct idxd_wq {
 	struct sbitmap_queue sbq;
 	struct dma_chan dma_chan;
 	char name[WQ_NAME_SIZE + 1];
+	u64 max_xfer_bytes;
 };
 
 struct idxd_engine {

drivers/dma/idxd/init.c

@@ -176,6 +176,7 @@ static int idxd_setup_internals(struct idxd_device *idxd)
 		wq->idxd = idxd;
 		mutex_init(&wq->wq_lock);
 		wq->idxd_cdev.minor = -1;
+		wq->max_xfer_bytes = idxd->max_xfer_bytes;
 	}
 
 	for (i = 0; i < idxd->max_engines; i++) {

drivers/dma/idxd/sysfs.c

@@ -1064,6 +1064,45 @@ static ssize_t wq_cdev_minor_show(struct device *dev,
 static struct device_attribute dev_attr_wq_cdev_minor =
 		__ATTR(cdev_minor, 0444, wq_cdev_minor_show, NULL);
 
+static ssize_t wq_max_transfer_size_show(struct device *dev, struct device_attribute *attr,
+					 char *buf)
+{
+	struct idxd_wq *wq = container_of(dev, struct idxd_wq, conf_dev);
+
+	return sprintf(buf, "%llu\n", wq->max_xfer_bytes);
+}
+
+static ssize_t wq_max_transfer_size_store(struct device *dev, struct device_attribute *attr,
+					  const char *buf, size_t count)
+{
+	struct idxd_wq *wq = container_of(dev, struct idxd_wq, conf_dev);
+	struct idxd_device *idxd = wq->idxd;
+	u64 xfer_size;
+	int rc;
+
+	if (wq->state != IDXD_WQ_DISABLED)
+		return -EPERM;
+
+	rc = kstrtou64(buf, 0, &xfer_size);
+	if (rc < 0)
+		return -EINVAL;
+
+	if (xfer_size == 0)
+		return -EINVAL;
+
+	xfer_size = roundup_pow_of_two(xfer_size);
+	if (xfer_size > idxd->max_xfer_bytes)
+		return -EINVAL;
+
+	wq->max_xfer_bytes = xfer_size;
+
+	return count;
+}
+
+static struct device_attribute dev_attr_wq_max_transfer_size =
+		__ATTR(max_transfer_size, 0644,
+		       wq_max_transfer_size_show, wq_max_transfer_size_store);
+
 static struct attribute *idxd_wq_attributes[] = {
 	&dev_attr_wq_clients.attr,
 	&dev_attr_wq_state.attr,
@@ -1074,6 +1113,7 @@ static struct attribute *idxd_wq_attributes[] = {
 	&dev_attr_wq_type.attr,
 	&dev_attr_wq_name.attr,
 	&dev_attr_wq_cdev_minor.attr,
+	&dev_attr_wq_max_transfer_size.attr,
 	NULL,
 };