scsi: core: Detect support for command duration limits

Introduce the function scsi_cdl_check() to detect if a device supports
command duration limits (CDL). Support for the READ 16, WRITE 16, READ 32
and WRITE 32 commands are checked using the function scsi_report_opcode()
to probe the rwcdlp and cdlp bits as they indicate the mode page defining
the command duration limits descriptors that apply to the command being
tested.

If any of these commands support CDL, the field cdl_supported of struct
scsi_device is set to 1 to indicate that the device supports CDL.

Support for CDL for a device is advertizes through sysfs using the new
cdl_supported device attribute. This attribute value is 1 for a device
supporting CDL and 0 otherwise.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Co-developed-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Link: https://lore.kernel.org/r/20230511011356.227789-9-nks@flawful.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 81 insertions, 0 deletions

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 62d9472e08e9..c03814ce23ca 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -570,6 +570,87 @@ int scsi_report_opcode(struct scsi_device *sdev, unsigned char *buffer,
 }
 EXPORT_SYMBOL(scsi_report_opcode);
 
+#define SCSI_CDL_CHECK_BUF_LEN	64
+
+static bool scsi_cdl_check_cmd(struct scsi_device *sdev, u8 opcode, u16 sa,
+			       unsigned char *buf)
+{
+	int ret;
+	u8 cdlp;
+
+	/* Check operation code */
+	ret = scsi_report_opcode(sdev, buf, SCSI_CDL_CHECK_BUF_LEN, opcode, sa);
+	if (ret <= 0)
+		return false;
+
+	if ((buf[1] & 0x03) != 0x03)
+		return false;
+
+	/* See SPC-6, one command format of REPORT SUPPORTED OPERATION CODES */
+	cdlp = (buf[1] & 0x18) >> 3;
+	if (buf[0] & 0x01) {
+		/* rwcdlp == 1 */
+		switch (cdlp) {
+		case 0x01:
+			/* T2A page */
+			return true;
+		case 0x02:
+			/* T2B page */
+			return true;
+		}
+	} else {
+		/* rwcdlp == 0 */
+		switch (cdlp) {
+		case 0x01:
+			/* A page */
+			return true;
+		case 0x02:
+			/* B page */
+			return true;
+		}
+	}
+
+	return false;
+}
+
+/**
+ * scsi_cdl_check - Check if a SCSI device supports Command Duration Limits
+ * @sdev: The device to check
+ */
+void scsi_cdl_check(struct scsi_device *sdev)
+{
+	bool cdl_supported;
+	unsigned char *buf;
+
+	buf = kmalloc(SCSI_CDL_CHECK_BUF_LEN, GFP_KERNEL);
+	if (!buf) {
+		sdev->cdl_supported = 0;
+		return;
+	}
+
+	/* Check support for READ_16, WRITE_16, READ_32 and WRITE_32 commands */
+	cdl_supported =
+		scsi_cdl_check_cmd(sdev, READ_16, 0, buf) ||
+		scsi_cdl_check_cmd(sdev, WRITE_16, 0, buf) ||
+		scsi_cdl_check_cmd(sdev, VARIABLE_LENGTH_CMD, READ_32, buf) ||
+		scsi_cdl_check_cmd(sdev, VARIABLE_LENGTH_CMD, WRITE_32, buf);
+	if (cdl_supported) {
+		/*
+		 * We have CDL support: force the use of READ16/WRITE16.
+		 * READ32 and WRITE32 will be used for devices that support
+		 * the T10_PI_TYPE2_PROTECTION protection type.
+		 */
+		sdev->use_16_for_rw = 1;
+		sdev->use_10_for_rw = 0;
+
+		sdev->cdl_supported = 1;
+	} else {
+		sdev->cdl_supported = 0;
+	}
+
+	kfree(buf);
+}
+
 /**
  * scsi_device_get  -  get an additional reference to a scsi_device
  * @sdev:	device to get a reference to