[PATCH v2 05/11] scsi-disk: add SCSI_DISK_QUIRK_MODE_SENSE_ROM_FORCE_DBD quirk for Macintosh

[Mark Cave-Ayland]

During SCSI bus enumeration A/UX sends a MODE SENSE command to the CDROM and
expects the response to include a block descriptor. As per the latest SCSI
documentation, QEMU currently force-disables the block descriptor for CDROM
devices but the A/UX driver expects the block descriptor to always be
returned.

If the block descriptor is not returned in the response then A/UX becomes
confused, since the block descriptor returned in the MODE SENSE response is
used to generate a subsequent MODE SELECT command which is then invalid.

Add a new SCSI_DISK_QUIRK_MODE_SENSE_ROM_FORCE_DBD to allow this behaviour
to be enabled as required.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
---
 hw/scsi/scsi-disk.c    | 18 +++++++++++++-----
 include/hw/scsi/scsi.h |  1 +
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 5de4506b97..71fdf132c1 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -1279,10 +1279,17 @@ static int scsi_disk_emulate_mode_sense(SCSIDiskReq *r, 
uint8_t *outbuf)
             dev_specific_param |= 0x80; /* Readonly.  */
         }
     } else {
-        /* MMC prescribes that CD/DVD drives have no block descriptors,
-         * and defines no device-specific parameter.  */
-        dev_specific_param = 0x00;
-        dbd = true;
+        if (s->quirks & (1 << SCSI_DISK_QUIRK_MODE_SENSE_ROM_FORCE_DBD)) {
+            dev_specific_param = 0x00;
+            dbd = false;
+        } else {
+            /*
+             * MMC prescribes that CD/DVD drives have no block descriptors,
+             * and defines no device-specific parameter.
+             */
+            dev_specific_param = 0x00;
+            dbd = true;
+        }
     }
 
     if (r->req.cmd.buf[0] == MODE_SENSE) {
@@ -1578,7 +1585,6 @@ static void scsi_disk_emulate_mode_select(SCSIDiskReq *r, 
uint8_t *inbuf)
     /* Ensure no change is made if there is an error!  */
     for (pass = 0; pass < 2; pass++) {
         if (mode_select_pages(r, p, len, pass == 1) < 0) {
-            assert(pass == 0);
             return;
         }
     }
@@ -3107,6 +3113,8 @@ static Property scsi_cd_properties[] = {
                        DEFAULT_MAX_IO_SIZE),
     DEFINE_PROP_INT32("scsi_version", SCSIDiskState, qdev.default_scsi_version,
                       5),
+    DEFINE_PROP_BIT("quirk_mode_sense_rom_force_dbd", SCSIDiskState, quirks,
+                    SCSI_DISK_QUIRK_MODE_SENSE_ROM_FORCE_DBD, 0),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/include/hw/scsi/scsi.h b/include/hw/scsi/scsi.h
index 975d462347..a9e657e03c 100644
--- a/include/hw/scsi/scsi.h
+++ b/include/hw/scsi/scsi.h
@@ -228,5 +228,6 @@ extern const SCSIReqOps scsi_generic_req_ops;
 
 /* scsi-disk.c */
 #define SCSI_DISK_QUIRK_MODE_PAGE_APPLE_VENDOR     0
+#define SCSI_DISK_QUIRK_MODE_SENSE_ROM_FORCE_DBD   1
 
 #endif
-- 
2.20.1