scsi: core: Allow enabling and disabling command duration limits

Add the sysfs scsi_device attribute cdl_enable to allow a user to enable or
disable a device command duration limits feature. CDL is disabled by
default. This feature must be explicitly enabled by a user by setting the
cdl_enable attribute to 1.

The new function scsi_cdl_enable() does not do anything beside setting the
cdl_enable field of struct scsi_device in the case of a (real) SCSI device
(e.g. a SAS HDD). For ATA devices, the command duration limits feature
needs to be enabled/disabled using the ATA feature sub-page of the control
mode page. To do so, the scsi_cdl_enable() function checks if this mode
page is supported using scsi_mode_sense(). If it is, scsi_mode_select() is
used to enable and disable CDL.

Signed-off-by: Damien Le Moal <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Co-developed-by: Niklas Cassel <[e-mail]>
Signed-off-by: Niklas Cassel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

Documentation/ABI/testing/sysfs-block-device

···
 Description:
 		(RO) Indicates if the device supports the command duration
 		limits feature found in some ATA and SCSI devices.
+
+
+What:		/sys/block/*/device/cdl_enable
+Date:		May, 2023
+KernelVersion:	v6.5
+Contact:	[e-mail]
+Description:
+		(RW) For a device supporting the command duration limits
+		feature, write to the file to turn on or off the feature.
+		By default this feature is turned off.
+		Writing "1" to this file enables the use of command duration
+		limits for read and write commands in the kernel and turns on
+		the feature on the device. Writing "0" disables the feature.

drivers/scsi/scsi.c

···
 }
 
 /**
+ * scsi_cdl_enable - Enable or disable a SCSI device supports for Command
+ *                   Duration Limits
+ * @sdev: The target device
+ * @enable: the target state
+ */
+int scsi_cdl_enable(struct scsi_device *sdev, bool enable)
+{
+	struct scsi_mode_data data;
+	struct scsi_sense_hdr sshdr;
+	struct scsi_vpd *vpd;
+	bool is_ata = false;
+	char buf[64];
+	int ret;
+
+	if (!sdev->cdl_supported)
+		return -EOPNOTSUPP;
+
+	rcu_read_lock();
+	vpd = rcu_dereference(sdev->vpd_pg89);
+	if (vpd)
+		is_ata = true;
+	rcu_read_unlock();
+
+	/*
+	 * For ATA devices, CDL needs to be enabled with a SET FEATURES command.
+	 */
+	if (is_ata) {
+		char *buf_data;
+		int len;
+
+		ret = scsi_mode_sense(sdev, 0x08, 0x0a, 0xf2, buf, sizeof(buf),
+				      5 * HZ, 3, &data, NULL);
+		if (ret)
+			return -EINVAL;
+
+		/* Enable CDL using the ATA feature page */
+		len = min_t(size_t, sizeof(buf),
+			    data.length - data.header_length -
+			    data.block_descriptor_length);
+		buf_data = buf + data.header_length +
+			data.block_descriptor_length;
+		if (enable)
+			buf_data[4] = 0x02;
+		else
+			buf_data[4] = 0;
+
+		ret = scsi_mode_select(sdev, 1, 0, buf_data, len, 5 * HZ, 3,
+				       &data, &sshdr);
+		if (ret) {
+			if (scsi_sense_valid(&sshdr))
+				scsi_print_sense_hdr(sdev,
+					dev_name(&sdev->sdev_gendev), &sshdr);
+			return ret;
+		}
+	}
+
+	sdev->cdl_enable = enable;
+
+	return 0;
+}
+
+/**
  * scsi_device_get  -  get an additional reference to a scsi_device
  * @sdev:	device to get a reference to
  *

drivers/scsi/scsi_sysfs.c

···
 		   sdev_show_queue_ramp_up_period,
 		   sdev_store_queue_ramp_up_period);
 
+static ssize_t sdev_show_cdl_enable(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(dev);
+
+	return sysfs_emit(buf, "%d\n", (int)sdev->cdl_enable);
+}
+
+static ssize_t sdev_store_cdl_enable(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf, size_t count)
+{
+	int ret;
+	bool v;
+
+	if (kstrtobool(buf, &v))
+		return -EINVAL;
+
+	ret = scsi_cdl_enable(to_scsi_device(dev), v);
+	if (ret)
+		return ret;
+
+	return count;
+}
+static DEVICE_ATTR(cdl_enable, S_IRUGO | S_IWUSR,
+		   sdev_show_cdl_enable, sdev_store_cdl_enable);
+
 static umode_t scsi_sdev_attr_is_visible(struct kobject *kobj,
 					 struct attribute *attr, int i)
 {
···
 #endif
 	&dev_attr_queue_ramp_up_period.attr,
 	&dev_attr_cdl_supported.attr,
+	&dev_attr_cdl_enable.attr,
 	REF_EVT(media_change),
 	REF_EVT(inquiry_change_reported),
 	REF_EVT(capacity_change_reported),

include/scsi/scsi_device.h

···
 	unsigned no_vpd_size:1;		/* No VPD size reported in header */
 
 	unsigned cdl_supported:1;	/* Command duration limits supported */
+	unsigned cdl_enable:1;		/* Enable/disable Command duration limits */
 
 	unsigned int queue_stopped;	/* request queue is quiesced */
 	bool offline_already;		/* Device offline message logged */
···
 extern int scsi_unregister_device_handler(struct scsi_device_handler *scsi_dh);
 void scsi_attach_vpd(struct scsi_device *sdev);
 void scsi_cdl_check(struct scsi_device *sdev);
+int scsi_cdl_enable(struct scsi_device *sdev, bool enable);
 
 extern struct scsi_device *scsi_device_from_queue(struct request_queue *q);
 extern int __must_check scsi_device_get(struct scsi_device *);