scsi: ufs: wb: Add explicit flush_threshold sysfs attribute

There are three flags that control Write Booster Feature:

    1. WB ON/OFF
    2. WB Hibern Flush ON/OFF (implicitly)
    3. WB Flush ON/OFF (explicit)

In the case of "Hibern Flush", one of the conditions for flush WB buffer is
that avail_wb_buff < wb_flush_threshold.

As we know, different users have different requirements for power
consumption and performance. Therefore, we need the ability to manually set
wb_flush_threshold, so that users can easily and flexibly adjust the
wb_flush_threshold value, thereby achieving a balance between power
consumption and performance.

So the sysfs attribute that controls this is necessary.

wb_flush_threshold represents the threshold for flushing WB buffer, whose
value expressed in unit of 10% granularity, such as '1' representing 10%,
'2' representing 20%, and so on.

Signed-off-by: Lu Hongfei <luhongfei@vivo.com>
Link: https://lore.kernel.org/r/20230613022240.16595-1-luhongfei@vivo.com
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Documentation/ABI/testing/sysfs-driver-ufs

@@ -1426,6 +1426,17 @@ Description:	This entry shows the status of WriteBooster buffer flushing
 		If flushing is enabled, the device executes the flush
 		operation when the command queue is empty.
 
+What:		/sys/bus/platform/drivers/ufshcd/*/wb_flush_threshold
+What:		/sys/bus/platform/devices/*.ufs/wb_flush_threshold
+Date:		June 2023
+Contact:	Lu Hongfei <luhongfei@vivo.com>
+Description:
+		wb_flush_threshold represents the threshold for flushing WriteBooster buffer,
+		whose value expressed in unit of 10% granularity, such as '1' representing 10%,
+		'2' representing 20%, and so on.
+		If avail_wb_buff < wb_flush_threshold, it indicates that WriteBooster buffer needs to
+		be flushed, otherwise it is not necessary.
+
 What:		/sys/bus/platform/drivers/ufshcd/*/device_descriptor/hpb_version
 What:		/sys/bus/platform/devices/*.ufs/device_descriptor/hpb_version
 Date:		June 2021

drivers/ufs/core/ufs-sysfs.c

@@ -298,6 +298,37 @@ out:
 	return res < 0 ? res : count;
 }
 
+static ssize_t wb_flush_threshold_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	struct ufs_hba *hba = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%u\n", hba->vps->wb_flush_threshold);
+}
+
+static ssize_t wb_flush_threshold_store(struct device *dev,
+					  struct device_attribute *attr,
+					  const char *buf, size_t count)
+{
+	struct ufs_hba *hba = dev_get_drvdata(dev);
+	unsigned int wb_flush_threshold;
+
+	if (kstrtouint(buf, 0, &wb_flush_threshold))
+		return -EINVAL;
+
+	/* The range of values for wb_flush_threshold is (0,10] */
+	if (wb_flush_threshold > UFS_WB_BUF_REMAIN_PERCENT(100) ||
+	    wb_flush_threshold == 0) {
+		dev_err(dev, "The value of wb_flush_threshold is invalid!\n");
+		return -EINVAL;
+	}
+
+	hba->vps->wb_flush_threshold = wb_flush_threshold;
+
+	return count;
+}
+
 static DEVICE_ATTR_RW(rpm_lvl);
 static DEVICE_ATTR_RO(rpm_target_dev_state);
 static DEVICE_ATTR_RO(rpm_target_link_state);
@@ -307,6 +338,7 @@ static DEVICE_ATTR_RO(spm_target_link_state);
 static DEVICE_ATTR_RW(auto_hibern8);
 static DEVICE_ATTR_RW(wb_on);
 static DEVICE_ATTR_RW(enable_wb_buf_flush);
+static DEVICE_ATTR_RW(wb_flush_threshold);
 
 static struct attribute *ufs_sysfs_ufshcd_attrs[] = {
 	&dev_attr_rpm_lvl.attr,
@@ -318,6 +350,7 @@ static struct attribute *ufs_sysfs_ufshcd_attrs[] = {
 	&dev_attr_auto_hibern8.attr,
 	&dev_attr_wb_on.attr,
 	&dev_attr_enable_wb_buf_flush.attr,
+	&dev_attr_wb_flush_threshold.attr,
 	NULL
 };