lsi53c895a: Implement IRQ on reselection

The critical part of this change is how to deal with simultaneaous
generation of interrupts. The only (normal) case when this happens in
the emulation is near simultaneous reselection + selection. If selection
comes first, there is no problem, since the target attempting
reselection loses the arbitration (in the emulation it only means that
the reselect function will not be started). In the worst case the host
adapter is reselected, but the device driver already started a
selection, so we jump to the alternative address to handle the
situation.

The SCRIPTS code can trigger another interrupt to notify the driver that
the new task has to be postponed. I suppose that on real hardware there
is enough time after the reselection interrupt to set the SIP bit before
the next interrupt comes, so it would result in 2 stacked interrupts (a
SCSI and a DMA one). However, in the emulation there is no interrupt
stacking, so there is a good chance that the 2 interrupts will get to
the interrupt handler at the same time.

Nevertheless, it should not make a big difference in interrupt handling,
since in both cases both interrupts have to be fetched first, and after
that the new task (that failed during the selection phase) has to be
prepared/reset for a later restart, and the reconnected device has to be
serviced.

The changes do not modify the host adapter's behavior if this interrupt
is not enabled.

See also LSI53C895A technical manual, SCID and SIEN0.

Signed-off-by: Laszlo Ast <laszlo.ast@siemens-enterprise.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 40 insertions, 3 deletions

diff --git a/hw/lsi53c895a.c b/hw/lsi53c895a.c
index 7fed1d8664..ab0de86104 100644
--- a/hw/lsi53c895a.c
+++ b/hw/lsi53c895a.c
@@ -154,6 +154,9 @@ do { fprintf(stderr, "lsi_scsi: error: " fmt , ## __VA_ARGS__);} while (0)
 #define LSI_CCNTL1_DDAC      0x08
 #define LSI_CCNTL1_ZMOD      0x80
 
+/* Enable Response to Reselection */
+#define LSI_SCID_RRE      0x60
+
 #define LSI_CCNTL1_40BIT (LSI_CCNTL1_EN64TIBMV|LSI_CCNTL1_64TIMOD)
 
 #define PHASE_DO          0
@@ -272,6 +275,11 @@ typedef struct {
     uint32_t script_ram[2048];
 } LSIState;
 
+static inline int lsi_irq_on_rsl(LSIState *s)
+{
+    return (s->sien0 & LSI_SIST0_RSL) && (s->scid & LSI_SCID_RRE);
+}
+
 static void lsi_soft_reset(LSIState *s)
 {
     DPRINTF("Reset\n");
@@ -362,6 +370,7 @@ static int lsi_dma_64bit(LSIState *s)
 static uint8_t lsi_reg_readb(LSIState *s, int offset);
 static void lsi_reg_writeb(LSIState *s, int offset, uint8_t val);
 static void lsi_execute_script(LSIState *s);
+static void lsi_reselect(LSIState *s, uint32_t tag);
 
 static inline uint32_t read_dword(LSIState *s, uint32_t addr)
 {
@@ -382,6 +391,7 @@ static void lsi_stop_script(LSIState *s)
 
 static void lsi_update_irq(LSIState *s)
 {
+    int i;
     int level;
     static int last_level;
 
@@ -413,6 +423,17 @@ static void lsi_update_irq(LSIState *s)
         last_level = level;
     }
     qemu_set_irq(s->dev.irq[0], level);
+
+    if (!level && lsi_irq_on_rsl(s) && !(s->scntl1 & LSI_SCNTL1_CON)) {
+        DPRINTF("Handled IRQs & disconnected, looking for pending "
+                "processes\n");
+        for (i = 0; i < s->active_commands; i++) {
+            if (s->queue[i].pending) {
+                lsi_reselect(s, s->queue[i].tag);
+                break;
+            }
+        }
+    }
 }
 
 /* Stop SCRIPTS execution and raise a SCSI interrupt.  */
@@ -607,6 +628,10 @@ static void lsi_reselect(LSIState *s, uint32_t tag)
     if (n != s->active_commands) {
         s->queue[n] = s->queue[s->active_commands];
     }
+
+    if (lsi_irq_on_rsl(s)) {
+        lsi_script_scsi_interrupt(s, LSI_SIST0_RSL, 0);
+    }
 }
 
 /* Record that data is available for a queued command.  Returns zero if
@@ -622,7 +647,14 @@ static int lsi_queue_tag(LSIState *s, uint32_t tag, uint32_t arg)
                 BADF("Multiple IO pending for tag %d\n", tag);
             }
             p->pending = arg;
-            if (s->waiting == 1) {
+            /* Reselect if waiting for it, or if reselection triggers an IRQ
+               and the bus is free.
+               Since no interrupt stacking is implemented in the emulation, it
+               is also required that there are no pending interrupts waiting
+               for service from the device driver. */
+            if (s->waiting == 1 ||
+                (lsi_irq_on_rsl(s) && !(s->scntl1 & LSI_SCNTL1_CON) &&
+                 !(s->istat0 & (LSI_ISTAT0_SIP | LSI_ISTAT0_DIP)))) {
                 /* Reselect device.  */
                 lsi_reselect(s, tag);
                 return 0;
@@ -659,10 +691,13 @@ static void lsi_command_complete(SCSIBus *bus, int reason, uint32_t tag,
         return;
     }
 
-    if (s->waiting == 1 || tag != s->current_tag) {
+    if (s->waiting == 1 || tag != s->current_tag ||
+        (lsi_irq_on_rsl(s) && !(s->scntl1 & LSI_SCNTL1_CON))) {
         if (lsi_queue_tag(s, tag, arg))
             return;
     }
+
+    /* host adapter (re)connected */
     DPRINTF("Data ready tag=0x%x len=%d\n", tag, arg);
     s->current_dma_len = arg;
     s->command_complete = 1;
@@ -1071,7 +1106,9 @@ again:
                 s->scntl1 &= ~LSI_SCNTL1_CON;
                 break;
             case 2: /* Wait Reselect */
-                lsi_wait_reselect(s);
+                if (!lsi_irq_on_rsl(s)) {
+                    lsi_wait_reselect(s);
+                }
                 break;
             case 3: /* Set */
                 DPRINTF("Set%s%s%s%s\n",