[PATCH v8 1/6] ata: libata-scsi: add atapi_max_lun module parameter

Until now libata has hard-coded shost->max_lun = 1 for every ATA host,
so the SCSI layer never scans past LUN 0.  This blocks support for
the small handful of multi-LUN ATAPI devices (Panasonic LF-1195C and
COMPAQ PD-1 PD/CD combos export CD on LUN 0 and PD on LUN 1; old
Nakamichi MJ-x.y CD changers expose one LUN per disc slot, up to 7).

Introduce a libata module parameter, atapi_max_lun, that controls the
upper bound of the per-host SCSI LUN scan.  Default is 1, preserving
current behaviour exactly: out-of-the-box only LUN 0 is scanned.
Range is clamped to 1..ATAPI_MAX_LUN (8, the SCSI-2 ceiling, covering
LUN values 0..7).

Subsequent patches gate actual LUN>0 probing on BLIST_FORCELUN, so a
device must both be on the SCSI device list (or carry the appropriate
quirk) and run on a host whose atapi_max_lun has been raised before
any extra LUNs are scanned.

Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Signed-off-by: Phil Pemberton <[email protected]>
---
 drivers/ata/libata-core.c | 5 +++++
 drivers/ata/libata-scsi.c | 2 +-
 drivers/ata/libata.h      | 1 +
 include/linux/libata.h    | 1 +
 4 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index d893c916df0b..15ee44cf5bf2 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -122,6 +122,11 @@ int atapi_passthru16 = 1;
 module_param(atapi_passthru16, int, 0444);
 MODULE_PARM_DESC(atapi_passthru16, "Enable ATA_16 passthru for ATAPI devices (0=off, 1=on [default])");
 
+int atapi_max_lun = 1;
+module_param(atapi_max_lun, int, 0444);
+MODULE_PARM_DESC(atapi_max_lun,
+	"Number of LUNs to scan on ATAPI devices flagged BLIST_FORCELUN (1 [default] = LUN 0 only, 8 = all SCSI-2 LUNs 0..7)");
+
 int libata_fua = 0;
 module_param_named(fua, libata_fua, int, 0444);
 MODULE_PARM_DESC(fua, "FUA support (0=off [default], 1=on)");
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 1d225ee9eb86..04c96f3fd865 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -5154,7 +5154,7 @@ int ata_scsi_add_hosts(struct ata_host *host, const struct scsi_host_template *s
 		shost->transportt = &ata_scsi_transportt;
 		shost->unique_id = ap->print_id;
 		shost->max_id = 16;
-		shost->max_lun = 1;
+		shost->max_lun = clamp(atapi_max_lun, 1, ATAPI_MAX_LUN);
 		shost->max_channel = 1;
 		shost->max_cmd_len = 32;
 
diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
index 39494ab206a2..7ee3bf1a4789 100644
--- a/drivers/ata/libata.h
+++ b/drivers/ata/libata.h
@@ -33,6 +33,7 @@ enum {
 #define ATA_PORT_TYPE_NAME	"ata_port"
 
 extern int atapi_passthru16;
+extern int atapi_max_lun;
 extern int libata_fua;
 extern int libata_noacpi;
 extern int libata_allow_tpm;
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 18edb36c29fc..25e4b671adfb 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -180,6 +180,7 @@ enum {
 	ATA_SHORT_PAUSE		= 16,
 
 	ATAPI_MAX_DRAIN		= 16 << 10,
+	ATAPI_MAX_LUN		= 8,	/* SCSI-2 cap (LUN values 0..7) */
 
 	ATA_ALL_DEVICES		= (1 << ATA_MAX_DEVICES) - 1,
 
-- 
2.43.0